Ahad Yusufi

Sodium nitroprusside (SNP) is an antihypertensive drug with proven toxic effects attributed mainly to the production of nitric oxide (NO). Polyunsaturated fatty acids (PUFAs) are widely regarded as functional foods and have been shown to ameliorate the harmful effects of many toxicants. This study examined whether feeding of fish oil (FO)/flaxseed oil (FXO) would have any protective effect against SNP-induced hepatotoxicity and cell death. Male Wistar rats were fed either on normal diet or with 15% FO/FXO for 15 days, following which SNP (1.5 mg/kg body weight) was administered intraperitoneally for 7 days. Animals were killed after treatment, and livers were collected for further analysis. We observed that SNP significantly elevated tissue nitrite levels and lipid peroxidation (LPO) with concomitant perturbation in antioxidant defense systems accompanied with dysregulated glucose metabolism and pronounced cellular death. FO/FXO supplementation to SNP-treated rats caused reversal of...

Ramadan fasting is a unique model of fasting in which Muslims the world over abstain from food and water from dawn to sunset for 1 month. We hypothesized that this model of prolonged intermittent fasting would result in specific adaptive alterations in rat kidney to keep a positive balance of metabolites and inorganic phosphate (Pi). The effect of Ramadan-type fasting was studied on enzymes of carbohydrate metabolism and brush border membrane (BBM) and BBM uptake of 32Pi in different renal tissue zones in the rat model. Rats were fasted (12 h) and then re-fed (12 h) daily for 30 d similar to human Ramadan fasting. Ramadan-type fasting resulted in increased serum Pi and phospholipids, whereas Pi clearance decreased. Serum creatinine and its clearance were not affected. Fasting caused a significant decrease in the activities of lactate and malate dehydrogenases, glucose-6-phosphatase and fructose-1,6-bisphosphatase, both in the renal cortex and medulla. However, the activity of glucos...

The mechanism whereby thyroid hormones modulate the transport properties of luminal brush border membrane (BBM) of renal proximal tubules was studied in thyroparathyroidectomized rats. Administration of both T4 and T3 increased BBM capacity for Na+ gradient-dependent uptake of phosphate (Pi) by BBM vesicles (BBMV). This effect of thyroid hormones was present in thyroparathyroidectomized and hypophysectomized rats, and it was not blocked by a saturating dose of propranolol. The stimulatory effect of T3 and T4 on BBM transport of Pi was dose dependent in the range of 5.2-520 nmol/100 g BW. Pretreatment of rats with inhibitors of 5'-monodeiodinase (5'-DI), iopanoic acid or ipodate, prevented the increase in serum T3 in rats injected with T4, but it did not diminish the increase in BBM transport of Pi. Administration of iopanoic acid and ipodate also prevented a 5-fold increase in 5'-DI activity in renal cortical tissue elicited by T4 administration. Treatment with T3 resulted in an increase of Pi transport across BBM from kidneys of rats subjected to dietary Pi deprivation due either to total fasting or to feeding of a low Pi diet. Further, T3 administration enhanced amiloride-sensitive Na+-H+ countertransport across BBM, but the uptake of 22Na+ by BBMV in the absence of pH gradient was not changed. The Na+ gradient-dependent uptake of L-[3H]proline by BBMV was slightly decreased, but the uptake of [14C]citrate was not changed in response to T3. Administration of T3 increased Pi transport in BBMV prepared from juxtamedullary cortex, but not in BBMV from superficial cortex. Conversely, the rate of Na+-H+ countertransport was enhanced, and the enzymatic activity of alkaline phosphatase was decreased in BBMV from superficial cortex; no changes in these parameters were found in BBMV from juxtamedullary cortex. Our results indicate that the stimulatory effect of administered T3 and/or T4 on renal BBM transport of Pi is distinct from the modulatory effect of dietary Pi intake and is not secondary to the beta-effect of catecholamines or to altered secretion of GH. Both T3 and T4 elicit the increase in BBM transport of Pi in a similar manner; T4 is effective even after profound inhibition of in vivo conversion of T4 to T3 by potent 5'-DI inhibitors. Administration of T3 stimulates Na+ gradient-dependent Pi uptake only in BBMV prepared from the juxtamedullary zone, and it stimulates the H+-Na+ countertransport only in BBMV from the outer cortical zone. These findings indicate that thyroid hormones modulate the two distinct transport functions of BBM derived from two different populations of renal proximal tubules.

Recent studies in cultured cells have provided evidence that a variety of pathobiologic stimuli, including high glucose, angio- tensin II, and thromboxane A2, trigger a signaling pathway lead- ing to autocrine induction of TGF-1. TGF-1 production through this pathway may profoundly affect cell growth, matrix synthesis, and response to injury. This study examines the role of autocrine versus exogenously added

Cisplatin (CDDP) is widely used in the treatment of various cancers but its clinical use is associated with dose limiting nephrotoxicity. The present work was carried out to study the effect of administration of CDDP on rat renal brush border membrane (BBM) marker enzymes and inorganic phosphate (Pi) transport across BBM vesicles (BBMV). Animals were administered a single intraperitoneal dose of CDDP (6 mg/kg body weight) or normal saline and then sacrificed 2, 4, 8 and 16 days after this treatment. The administration of CDDP resulted in increased serum creatinine and blood urea nitrogen levels and decreased activity of BBM marker enzymes in the BBM as well as in the homogenates of cortex and medulla. Kinetic studies showed that the Vmax of the enzymes was decreased in BBM from CDDP treated rats while the Km remained unchanged. The Na+-gradient dependent transport of Pi across BBMV was also significantly reduced after CDDP treatment. These results strongly suggest that the administration of a single nephrotoxic dose of CDDP results in impairment of the functions of renal BBM.

Cisplatin (CDDP) is widely used in the treatment of various cancers but its clinical use is associated with dose limiting nephrotoxicity. The present work was carried out to study the effect of administration of CDDP on rat renal brush border membrane (BBM) marker enzymes and inorganic phosphate (Pi) transport across BBM vesicles (BBMV). Animals were administered a single intraperitoneal dose of CDDP (6 mg/kg body weight) or normal saline and then sacrificed 2, 4, 8 and 16 days after this treatment. The administration of CDDP resulted in increased serum creatinine and blood urea nitrogen levels and decreased activity of BBM marker enzymes in the BBM as well as in the homogenates of cortex and medulla. Kinetic studies showed that the Vmax of the enzymes was decreased in BBM from CDDP treated rats while the Km remained unchanged. The Na+-gradient dependent transport of Pi across BBMV was also significantly reduced after CDDP treatment. These results strongly suggest that the administration of a single nephrotoxic dose of CDDP results in impairment of the functions of renal BBM.

Gentamicin (GM), an antibiotic against life threatening bacterial infection, induces remarkable toxicity in the kidney. Histological studies have indicated that mitochondria, microsomes, lysosomes and plasma membranes of renal proximal convoluted tubules in particular are major GM targets. Despite numerous investigations, the biochemical/cellular basis of GM nephrotoxicity is not well understood. Recently reactive oxygen species (ROS) are considered to be important mediators of GM-induced nephrotoxicity. We hypothesize that GM causes damage to intracellular organelles and affects their structural integrity and alters metabolic and other functional capabilities. To address above hypothesis a long-term, time-dependent effect of GM has been studied on blood/urine parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM) and basolateral (BLM), lysosomes and oxidative stress in renal tissues. A nephrotoxic dose of GM (80 mg/kg body weight) was administered to rats daily...

Gentamicin (GM), an antibiotic against life threatening bacterial infection, induces remarkable toxicity in the kidney. Histological studies have indicated that mitochondria, microsomes, lysosomes and plasma membranes of renal proximal convoluted tubules in particular are major GM targets. Despite numerous investigations, the biochemical/cellular basis of GM nephrotoxicity is not well understood. Recently reactive oxygen species (ROS) are considered to be important mediators of GM-induced nephrotoxicity. We hypothesize that GM causes damage to intracellular organelles and affects their structural integrity and alters metabolic and other functional capabilities. To address above hypothesis a long-term, time-dependent effect of GM has been studied on blood/urine parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM) and basolateral (BLM), lysosomes and oxidative stress in renal tissues. A nephrotoxic dose of GM (80 mg/kg body weight) was administered to rats daily...

Guanylate cyclase (GCase) and cyclic guanosine 3'5'-monophosphate-phosphodiesterase (cGMP-PDE) activities were measured in the medulla, glomeruli and cortical tubules isolated from the remaining kidney 5-120 min after unilateral nephrectomy. The results showed that cGMP-PDE-specific activities were unchanged in all the fractions isolated from the contralateral kidney when compared with the nephrectomized control kidney. The GCase-specific activity in the cortical and medullary tubules isolated from the remaining kidney reached a maximum by 10 min after unilateral nephrectomy and then returned to control values. On the other hand the glomerular GCase activity decreased for 10 min after unilateral nephrectomy, then rebound activity reached a maximum by 30 min and after 120 min had returned to the control value. The possible physiological signification of such variations is discussed.

Alkaline phosphatases from different trematodes occupying the same habitat have identical pH otima but different levels of enzyme activities. Isoparorchis hypselobagri, from the fish Wallago attu, shows four to six times more enzyme activity than Fasciolopsis buski, Gastrodiscoides hominis and Echinostoma malayanum, from the pig Sus scrofa, and Fasciola gigantica, Gigantocotyle explanatum, Cotylophoron cotylophorum and Gastrothylax crumenifer, from the buffalo Bubalus bubalis. At least two peaks of activity at different levels of pH were obtained for each trematode examined. Both Gastrodiscoides hominis and Isoparorchis hypselobagri enzymes had three peaks of alkaline phosphatase activity. The optimum temperature for maximum enzyme activity was 40 degrees C, above which rapid inactivation occurred. At temperatures below 40 degrees C, the enzymes of fish and mammalian trematodes did not behave similarly; I. hypselobagri enzyme being active over a wider range of temperature (20 degrees-40 degrees C. Various concentrations of KCN and arsenate proportionately inhibited enzyme activity. NaF Did not significantly influence enzyme activity, while Mg++ and Co++ acted as activators. The extent of inhibition or activation of enzyme activity of different trematodes varied, probably due to species differences. Both inhibition and activation of I. hypselobagri enzyme was higher than in the case of other trematodes.

To differentiate BBM from proximal convoluted tubules (PCT) and from pars recta (PR), the authors isolated separately membrane fractions from superficial cortex (SC-tissue) and from juxtamedullary cortex plus outer stripe of red medulla (JM-tissue) by centrifugation in Percoll gradient. BBM separated on Percoll gradient into the higher density zone (zone A), and lower density zone (zone B). The zone B

1. Adv Exp Med Biol. 1984;178:139-44. ATP as a factor in the response of the cAMP system to PTH in proximal and distal convoluted tubules. Dousa TP, Kiebzak GM, Yusufi AN, Kusano E, Braun-Werness J. PMID: 6095614 [PubMed - indexed for MEDLINE]. Publication Types: ...

We examined the effect of phosphonoformic acid (PFA) and phosphonoacetic acid (PAA) upon Na+-Pi cotransport in brush-border membrane (BBM) from small gut of rat. Both PFA and PAA inhibited the Na+ gradient-dependent uptake of 32Pi by BBM vesicles (BBMV) prepared from intestinal mucosa but had no effect on Na+-dependent uptakes of D-[3H]glucose, L-[3H]proline, or [14C]succinate. The uptake in the absence of Na+ gradient, or uptake at equilibrium period (180 min), was not affected by PFA or by PAA. A chemical analogue of PFA and PAA, phosphonopropionic acid, had only a minor inhibitory effect and phenylphosphonic acid was inactive. Neither PFA nor PAA influenced the activity of rat intestinal BBM alkaline phosphatase. The BBMV from rat jejunum had a much higher capacity for Na+ gradient-dependent uptake of 32Pi than BBMV from duodenum or ileum. The inhibition of BBMV 32Pi transport across rat jejunum by PFA is competitive. We suggest that PFA and PAA are specific inhibitors of Na+ gradient-dependent uptake of Pi by BBMV from small intestinal mucosa and that they could serve as useful experimental tools for the studies of intestinal Na+-Pi cotransport.

NAD content and the rate of NAD hydrolysis were determined in proximal convoluted tubules (PCT), proximal straight tubules (PST), and adjacent cortical nephron segments microdissected from kidneys of thyroparathyroidectomized (TPTX) rats. In the basal state, rats fed a normal phosphate diet had an NAD content higher in PCT, PST, and in cortical ascending limb (CAL) than in glomeruli. After intraperitoneal injection of nicotinamide, the NAD content increased significantly in all nephron segments except CAL; the greatest (delta + 277%) increase was found in PCT, with less (delta + 82%) in PST. In experiments conducted on TPTX rats stabilized on a low-phosphorus diet, NAD content increased in response to a nicotinamide injection in PCT (delta + 197%), but did not change significantly in PST. The catabolism of NAD was determined by generation of [3H]adenosine, a major metabolite of [adenine-2,8-3H]NAD. The rate of [3H]adenosine generation from [3H]NAD was significantly (P less than 0.001) higher in PST than in PCT. We conclude that, in response to nicotinamide administration in vivo, the NAD content increases more in PCT than in PST and that this difference may be, at least partly, due to a lower rate of NAD breakdown in PCT. In a state of dietary phosphate deprivation, NAD also increases significantly in response to intraperitoneal nicotinamide in PCT, but it does not increase significantly in PST. The nicotinamide-elicited increase of NAD content in proximal tubules, mainly in PCT, may be related to inhibition of Na+-gradient-dependent inorganic phosphate (Pi) reabsorption across the brush-border membrane of proximal tubules and to the phosphaturic effect of nicotinamide in rats fed normal-Pi diet.

In mice with hereditary nephrogenic diabetes insipidus (NDI), the high activity of cAMP-phosphodiesterase (cAMP-PDIE) in medullary collecting tubules (MCT) prevents the increase in cAMP content in response to vasopressin [Arg8]vasopressin (AVP). Even when the cAMP response to AVP is partly corrected by cAMP-PDIE inhibitor 1-methyl-3-isobutylxanthine (MIX), under all tested conditions the cAMP levels in MCT of NDI mice remained much lower than in controls (B. A. Jackson, R. M. Edwards, H. Valtin, and T. P. Dousa, J. Clin. Invest. 66: 110-122, 1980). In the present study, we explored which factors may account for this defect. We determined contents of ATP, nicotinamide adenine dinucleotide (NAD), and the levels of cAMP in MCT and in medullary thick ascending limb of Henle's loop (MAL) microdissected from control and NDI mice. In the presence of 1 microM AVP and 0.05 mM MIX, the cAMP levels accumulated in MCT of NDI mice were four times lower compared with controls, but the levels of ATP and NAD were not different. ATP levels in MAL of NDI mice were slightly (delta -23%) lower than in MAL from controls, and in distal convoluted tubules (DCT) of NDI mice the ATP levels were also decreased (delta -49%). Although AVP alone had little effect on cAMP levels in mouse MAL in the presence of 0.1 mM forskolin, the AVP elicited a 20-fold increase of cAMP of both the control and NDI mice. Addition of 0.1 mM forskolin further increased the cAMP accumulation in MCT incubated with AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

The modulatory effect of Ca on [Arg8]vasopressin-dependent (AVP) cAMP metabolism was studied in medullary collecting tubules (MCT) and medullary ascending limbs (MAL) microdissected from rat kidney. In MCT segments incubated in vitro with AVP, the accumulation of cAMP was enhanced (delta +59%) when Ca was omitted from the incubation medium compared with a medium with 2 mM of ionized calcium (Ca2+). Ionophore A23187 caused a decrease in AVP-stimulated cAMP accumulation in MCT in the presence of 2 mM Ca2+ but not in a Ca2+-free medium. Diltiazem and verapamil enhanced the AVP-stimulated cAMP accumulation in MCT; PTH had no detectable effect. A23187 caused a dose-dependent inhibition of cAMP accumulation stimulated by AVP with forskolin in both MCT and in MAL. However, in MAL the A23187 concentration needed for half-maximum inhibition (6.3 X 10(-6) M) was higher than for MCT (3.9 X 10(-7) M). The maximum inhibition in MAL (-65%) was less than in MCT (-97%). In the presence of 3-isobutyl-1-methylxanthine, AVP-stimulated cAMP accumulation was inhibited by A23187 in MCT (-45%) but not in MAL. Naproxen or ibuprofen did not relieve the inhibitory action of A23187 in MCT. Added Ca2+ inhibited the AVP-stimulated adenylate cyclase in MCT and MAL (half-maximum approximately equal to 5 X 10(-4) M Ca2+) and stimulated cAMP phosphodiesterase (cAMP-PDIE) in both MCT and in MAL (half-maximum approximately equal to 9 X 10(-5) M Ca2+). Incubation of MCT and MAL with A23187 decreased (-50%) the content of ATP. Results suggest that increased influx of extracellular Ca2+ inhibits the AVP-stimulated cAMP accumulation in MCT and to a much lesser degree in MAL. Deceased cAMP accumulation in MCT is probably due to both stimulation of cAMP-PDIE and the inhibition of adenylate cyclase, whereas in MAL it is due to stimulation of cAMP-PDIE. The results suggest that Ca2+ influx exhibits a negative modulatory effect on AVP-dependent cAMP metabolism mainly in MCT.

Responsiveness of proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) microdissected from mouse kidney to PTH, in terms of cAMP accumulation and stimulation of adenylate cyclase, was examined. In both PCT and DCT, the cell-free adenylate cyclase was stimulated at least 10-fold by the same dose (10 U/ml) of PTH, and activity of cAMP phosphodiesterase was about 80% higher in DCT than in PCT. In intact tubules, while the incubation with PTH increased cAMP content in DCT more than 10-fold, it failed to increase the cAMP levels in PCT. To explain discrepancies between cell-free and intact cell incubations, ATP content in microdissected tubules was determined with use of a microbioluminescence assay. ATP content in PCT (4.0 +/- 1.3 fmol/mm, n = 30) was dramatically lower than ATP content of DCT (376.8 +/- 54.3 fmol/mm, n = 25). Incubation with 1 microM rotenone reduced markedly (delta -98%) the ATP content in DCT. In DCT, with ATP depleted by 1 microM rotenone, PTH failed to increase the cAMP, although 1 microM rotenone did not inhibit the adenylate cyclase activity. When 0.1 mM of 1-methyl-3-isobutylxanthine (MIX) was added to the incubation medium, PTH caused a marked elevation in tubular cAMP in PCT and to even a greater degree in DCT. Present results show that various segments of microdissected tubules differ greatly in their ability to maintain adequate ATP levels for cAMP generation in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous studies showed that an increase in NAD+ content in renal cortex in vivo was accompanied by specific inhibition of Na+-dependent inorganic phosphate (Pi) transport across the renal brush border membrane (BBM). Further, in vitro addition of NAD+ to isolated renal BBM vesicles specifically inhibited Na+ gradient-dependent transport of Pi. The present study examined some aspects of the mechanism of this inhibition by NAD+ in vitro and in vivo. When NAD+ was increased in vivo by nicotinamide injection, the apparent Vmax was decreased, but the apparent Km was not different, indicating apparent noncompetitive inhibition. In the presence of 0.3 mM NAD+ added in vitro, the apparent Km for Na+-dependent Pi transport by BBM vesicles was increased, whereas the apparent Vmax was unchanged, indicating apparent competitive inhibition. These changes in apparent Km and apparent Vmax were identical when Pi uptake was measured either at 30-s or at 5-s (the initial rate) incubation times. Inhibition of Pi transport by BBM vesicles in vitro was due primarily to the action of intact added NAD+, although there may be some contribution by isotope dilution due to Pi released from NAD+ by enzymatic hydrolysis. Although in vitro inhibition of Pi transport by added NAD+ was reversed by washing the BBM, the inhibition due to increased NAD+ in vivo persisted after extensive washing of the isolated BBM. The specificity of the inhibitory effect of NAD+ in vivo was indicated by the finding that changes in renal cortical content of ATP or Pi, evoked by loading with glycerol or fructose, did not change BBM transport of Pi.(ABSTRACT TRUNCATED AT 250 WORDS)

This study was undertaken to determine whether calcitonin inhibits Na+-(Pi) cotransport across luminal brush-border membrane (BBM) of proximal tubules. Further, we determined the relative inhibitions of inorganic phosphate (Pi) transport in BBM vesicles (BBMV) derived from superficial cortical tissue (BBMV-SC) and juxtamedullary tissue (BBMV-JM). The effects of maximally phosphaturic doses of calcitonin were compared with those of parathyroid hormone (PTH). Experiments were performed in acutely thyroparathyroidectomized (TPTX) rats fed either normal (NPD, 0.7%) or low (LPD, 0.07%) Pi diets. After measurement of the fractional excretion of phosphate (FEPi) by clearance, the BBMV-SC and BBMV-JM were prepared from kidneys of the same animals and uptakes of 32Pi were determined. Both calcitonin and PTH inhibited BBMV transport of Pi to a greater degree in BBMV-JM than in BBMV-SC, in rats fed NPD or LPD. Kinetic analysis shows that administration of calcitonin resulted in marked decrease of apparent Vmax for Pi without any changes in apparent Km for Pi. However, in spite of a decreased capacity for Na+ gradient-dependent 32Pi uptake in BBMV-JM and much lesser in BBMV-SC in response to administration of calcitonin and PTH in Pi-deprived rats, these phosphaturic peptides did not increase FEPi. We conclude that calcitonin administration decreases the capacity for Na+-Pi cotransport across BBM in proximal tubules of the acutely TPTX rat.

In previous studies we found that intraperitoneal injection of nicotinamide (NiAm) to rats resulted in increased NAD+ content in proximal tubules, inhibition of brush border membrane (BBM) transport of phosphate (Pi) and decreased activity of alkaline phosphatase (AP). We now studied the effect of NiAm injection on rabbit kidney BBM prepared either directly by Ca2+ precipitation method, or prepared indirectly from sheets of BBM. In BBM vesicles prepared directly from NiAm-injected rabbits, Na+-dependent Pi uptake was inhibited, but no inhibition was found in BBM vesicles prepared by an indirect method. Incubation of both directly prepared BBM vesicles and of BBM sheets with phosphatidylinositol-specific phospholipase C (PI-PLC) released about 85% of AP from BBM. In BBM vesicles prepared indirectly from BBM sheets, incubation with PI-PLC increased by 100% the capacity for Pi transport, but PI-PLC had no effect on Pi transport if rabbits were injected with NiAm. On the other hand, incubation of directly prepared BBM vesicles with PI-PLC did not alter Pi transport capacity both in controls and in NiAm-treated rabbits, although it released AP. Treatment with NiAm decreases significantly AP activity both in BBM vesicles prepared directly or prepared indirectly from BBM sheets. These results suggest that NiAm-induced inhibition of BBM transport system for Pi is reversed by prolonged washing and incubation in the course of indirect preparation of BBM vesicles. Results also suggest that an increase in tissue NAD+ decreases susceptibility of BBM to treatment with PI-PLC in altering Pi transport. Removal of the majority of AP from BBM does not impair Na+-gradient-dependent Pi transport system.

... microdissected from rat kidney: effect of AVP SUMIKO HOMMA, SUSAN M. GAPSTUR, AHAD NK YUSUFI, AND THOMAS P. DOUSA Nephrology Research Unit, Departments of Medicine and Physiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905 ...

Signaling via release of Ca2+ from intracellular stores is mediated by several systems, including the inositol 1,4,5-trisphosphate (IP3) and cADP-ribose (cADPR) pathway. We recently discovered a high capacity for cADPR synthesis in rat glomeruli and cultured mesangial cells (MC). We sought to determine whether 1) cADPR synthesis in MC is regulated by cytokines and hormones, 2) ryanodine receptors (RyRs) are expressed in MC, and 3) Ca2+ is released through RyRs in response to cADPR. We found that ADP-ribosyl cyclase, a CD38-like enzyme that catalyzes cADPR synthesis, is upregulated in MC by tumor necrosis factor-alpha, interleukin-1beta, and all-trans retinoic acid (atRA). [3H]ryanodine binds to microsomal fractions from MC with high affinity in a Ca2+-dependent manner; binding is enhanced by specific RyR agonists and blocked by ruthenium red and cADPR. Western blot analysis confirmed the presence of RyR in MC. Release of 45Ca2+ from MC microsomes was stimulated by cADPR; release was blocked by ruthenium red and 8-bromo-cADPR. ADPR (non-cyclic) was without effect. In MC, TNF-alpha and atRA amplified the increment of cytoplasmic Ca2+ elicited by vasopressin. We conclude that MC possess elements of a novel ADP-ribosyl cyclase-->cADPR-->RyR-->Ca2+-release signaling pathway subject to regulation by proinflammatory cytokines and steroid superfamily hormones.

We explored the biochemical mechanism by which thyroid hormone (T3) and low-phosphate diet (LPD) cause an adaptive increase in Na+-Pi cotransport across renal brush-border membrane (BBM). The rate of Na+-Pi cotransport was determined by 32Pi uptake by BBM vesicles (BBMV), and the number of Na+-Pi symporters was assessed by binding of [14C]phosphonoformic acid (PFA) on BBMV. In BBMV of both T3-treated rats and LPD-fed rats, the Na+ gradient-dependent 32Pi uptake increased (Vmax increased; Km Pi was not changed). The Na+-dependent [14C]PFA binding on BBMV increased (higher Vmax, no change in Km PFA) in response to T3, but it remained unchanged in rats fed LPD. Both the increase of Na+-Pi cotransport and of Na+-dependent [14C]PFA binding in response to T3 were blocked by actinomycin D or cycloheximide. Addition of benzyl alcohol to BBMV in vitro increased Na+-Pi cotransport, but [14C]PFA binding did not change; the [3H]phlorizin binding and cotransports of other solutes decreased or did not change. The exposure of BBMV to cholesterol decreased Na+-Pi cotransport without changing [14C]PFA binding. We suggest that the adaptive increase of Na+-Pi cotransport elicited by T3 is due to an increase in number of Na+-Pi cotransporters in BBM. In contrast, in response to LPD the number of Na+-Pi cotransporters is unchanged, and the increased Na+-Pi cotransport is due to faster translocation of Na+ with Pi due to enhanced fluidity of BBM.

Recent studies in cultured cells have provided evidence that a variety of pathobiologic stimuli, including high glucose, angiotensin II, and thromboxane A(2), trigger a signaling pathway leading to autocrine induction of TGF-beta1. TGF-beta1 production through this pathway may profoundly affect cell growth, matrix synthesis, and response to injury. This study examines the role of autocrine versus exogenously added TGF-beta1 in cellular proliferation and collagen IV production, critical targets of TGF-beta1 signaling, using renal cells derived from TGF-beta1 knockout (KO) animals or wild-type (WT) controls. Growth of WT and KO cells was assessed by cell counting and [(3)H]thymidine uptake. Basal and TGF-beta1-stimulated collagen production was assessed by Northern and Western blotting; transcriptional activity of the alpha1(IV) collagen gene was assessed by transient transfection analysis. KO cells grew at a faster rate than WT cells carefully matched for plating density and passage ...

The release of Ca(2+) from intracellular stores is a fundamental element of signaling pathways involved in regulation of vascular tone, proliferation, apoptosis, and gene expression. Studies of sea urchin eggs have led to the identification of three functionally distinct Ca(2+) signaling pathways triggered by IP3, cADPR, and NAADP. The coexistence and functional relevance of these distinct intracellular Ca(2+) release systems has only been described in a few mammalian cell types. The purpose of this study was to determine whether the IP3, cADPR, and NAADP Ca(2+) release systems coexist in smooth muscle cells (SMC) and to determine the specificity of these intracellular Ca(2+) release pathways. Microsomes were prepared from rat aortic SMC (VSMC) and were loaded with 45Ca(2+). cADPR, NAADP, and IP3 induced Ca(2+) release from VSMC microsomes in a dose-dependent fashion. Heparin blocked only IP3-mediated Ca(2+) release, whereas the ryanodine channel inhibitors 8-Br-cADPR and ruthenium ...