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2010
Abstract Intracellular cAMP and Ca 2+ are involved in the regulation of steroidogenic activity in Leydig cells, which coordinate responses to luteinizing hormone (LH) and human chorionic gonadotropin (hCG). However, the identification of Ca 2+ entry implicated in Leydig cell steroidogenesis is not well defined. The objective of this study was to identify the type of Ca 2+ channel that affects Leydig cell steroidogenesis. In vitro steroidogenesis in the freshly dissociated Leydig cells of mice was induced by hCG incubation.
Journal of Endocrinology
Blocking L-type calcium channels reduced the threshold of cAMP-induced steroidogenic acute regulatory gene expression in MA-10 mouse Leydig cells2010 •
Molecular and Cellular Endocrinology
Steroidogenesis and steroidogenic gene expression in postnatal fetal rat Leydig cells2011 •
Mibefradil is a new cardiovascular drug with peculiar Ca++ antagonistic properties. The most remarkable feature of mibefradil is its unique relative selectivity for T type calcium channels, a property that has been proposed to explain in part the beneficial pharmacological and clinical profiles of this drug. In adrenal glomerulosa cells, aldosterone biosynthesis and secretion in response to angiotensin II or extracellular potassium is dependent on a sustained influx of Ca++ through T type Ca++ channels. The effect of mibefradil on the steroidogenic function of glomerulosa cells was therefore investigated. Using the patch clamp technique, we found that mibefradil inhibits selectively and in a concentration-dependent manner (IC50 = 3 microM)++ T type currents in bovine glomerulosa cells. In addition to this tonic (voltage independent) inhibition, the drug also induced a shift of the steady-state inactivation curve of these channels toward hyperpolarized voltages, contributing to its efficacy to prevent Ca++ influx into the cell through T type channels. Concomitantly, mibefradil reduced the cytosolic calcium responses to potassium and angiotensin II (as assessed with fluorescent probes), without affecting the capacitative Ca++ influx, and inhibited pregnenolone and aldosterone formation. This inhibition of steroidogenesis was not exclusively due to mibefradil action on voltage-operated Ca++ channels, because this agent also partially reduced steroid synthesis induced by adrenocorticotropic hormone or forskolin, two activators of the cyclic AMP pathway. In conclusion, mibefradil is highly effective in adrenal glomerulosa cells in reducing T type channel activity and aldosterone biosynthesis, two actions that should contribute to the beneficial effect of the drug in the treatment of hypertension
1985 •
1999 •
The steroidogenic acute regulatory (StAR) protein, a 30-kDa mitochondrial factor, is a key regulator of steroid hormone biosynthesis, facilitating the transfer of cholesterol from the outer to the inner mitochondrial membrane. StAR protein expression is restricted to steroidogenic tissues, and it responds to hormonal stimulation through different second messenger pathways. The present study was designed to explore the mechanisms of extracellular calcium (Ca2+) involved in the hCG-stimulated expression of StAR protein and steroidogenesis in a mouse Leydig tumor cell line (mLTC-1). Extracellular Ca2+ (1.5 mmol/liter) enhanced the hCG (50μ g/liter)-induced increases in StAR messenger RNA (mRNA) and protein levels (1.7 ± 0.3-fold; 4 h), as monitored by quantitative RT-PCR and immunoblotting. The potentiating effect of Ca2+ on the hCG-stimulated StAR response correlated with the acute progesterone (P) response. In accordance, omission of Ca2+ from the extracellular medium by specific Ca2...
Toxicology Letters
Acute effects of hexabromocyclododecane on Leydig cell cyclic nucleotide signaling and steroidogenesis in vitroAJP: Cell Physiology
A calcium-induced calcium release mechanism supports luteinizing hormone-induced testosterone secretion in mouse Leydig cells2010 •
Leydig cells are responsible for the synthesis and secretion of testosterone, processes controlled by luteinizing hormone (LH). Binding of LH to a G protein-coupled receptor in the plasma membrane results in an increase in cAMP and in intracellular Ca2+ concentration ([Ca2+]i). Here we show, using immunofluorescence, that Leydig cells express ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP3Rs). Measurements of intracellular calcium changes using the fluorescent calcium-sensitive dye fluo-3 and confocal microscopy show that both types of receptors are involved in a calcium-induced calcium release (CICR) mechanism, which amplifies the initial Ca2+ influx through plasma membrane T-type calcium channels (CaV3). The RyRs and IP3Rs are functional, as judged from both their activation by caffeine and IP3 and block by ryanodine and 2-aminoethoxydiphenyl borate (2-APB), respectively. RyRs are the principal players involved in the release of Ca2+ from the endoplasmic...
Journal of Molecular Endocrinology
Control of steroidogenesis by the calcium messenger system in human adrenocortical cells1991 •
Adolf Hitler Meinkampf romana
Adolf Hitler Meinkampf romanaAdolf Hitler Meinkampf romana
Conference Theme: Opening the Ancient World: Representations of the Past in Ancient & Modern Times This interdisciplinary conference examines exploration, representation, and reception of pasts in the broadest cross-cultural, global, and atemporal world context. This conference employs the framework of interdisciplinary “Ancient Studies,” the study of the deep past of all societies, exploring the reception and representation of the past in present and ancient societies. Removing the privileging of our contemporary temporal position by intertwining current and past explorations of pasts treats this issue as a human cultural construction in all societies. This free, public conference will be held on Sunday and Monday, July 21st to 22nd, 2024, and will be livestreamed on SASA’s website, social media channels, and on our partners’ platforms. For the first time, we are proud to announce that the Opening the Ancient World Virtual Conference will support live interpretation for Spanish and Arabic thanks to a grant from the Wenner-Gren Foundation!
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