In the present study, energetic and entropic changes are investigated on a comparative basis, as ... more In the present study, energetic and entropic changes are investigated on a comparative basis, as they occur in the volume changes of an ideal gas in the Carnot cycle and in the course of the chemical reaction in a lead-acid battery. Differences between reversible and irreversible processes have been worked out, in particular between reversibly exchanged entropy (e S ∆) and irreversibly produced entropy (i S ∆). In the partially irreversible case, e S ∆ and i S ∆ add up to the sum S ∆ for the volume changes of a gas, and only this function has an exact differential. In a chemical reaction, however, e S ∆ is independent on reversibility. It arises from the different intramolecular energy contents between products and reactants. Entropy production in a partially irreversible Carnot cycle is brought about through work-free expansions, whereas in the irreversible battery reaction entropy is produced via activated complexes, whereby a certain, variable fraction of the available chemical energy becomes transformed into electrical energy and the remaining fraction dissipated into heat. The irreversible reaction process via activated complexes has been explained phenomenologically. For a sufficiently high power output of coupled reactions, it is essential that the input energy is not completely reversibly transformed, but rather partially dissipated, because this can increase the process velocity and consequently its power output. A reduction of the counter potential is necessary for this purpose. This is not only important for man-made machines, but also for the viability of cells.
ATP delivery and its usage are achieved by cycling of respective intermediates through interconne... more ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill's equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca 2+ ]. Muscular fatigue is triggered when
A major goal of this study is to show how chemical and biochemical reactions occur. Since a large... more A major goal of this study is to show how chemical and biochemical reactions occur. Since a large part of the energy transformations occurring via a reaction is always related to changes in potential differences, these phenomenological events are initially also in the foreground. In addition to these energetic changes, however, entropic changes are also important. Here, special emphasis is placed on distinguishing between exchanged and produced entropy. The conversion of energy in chemical reactions into heat energy occupies a special position compared to the conversions of e.g. mechanical or electrical energy in that no forces are involved in the former. Using transport reactions through channels, the process can be expressed in a simplified form. It is made clear that heat generation occurs via energetic transition states, and that it is this generated heat itself that leads to a significant increase in multiplicity. As a result, the reaction process is allowed to take place. The conclusion is that in chemical and biochemical reactions, instead of a force, multiplicity determines the direction and course of such processes.
Journal of Molecular and Cellular Cardiology, Jun 1, 1995
Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective... more Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective conditions against the Ca2+ paradox. In addition sarcosolic free cation concentrations and the membrane potential were measured employing ion-selective microelectrode techniques during Ca(2+)-free perfusion. Low temperature (18 degrees C), low pH (6.5 or 6.1), and polyethylene glycol (9%) during Ca(2+)-free perfusion all protected isolated hearts against the Ca2+ paradox. Protection could only be afforded if the protective agent was continuously present from the beginning of the Ca(2+)-free perfusion period. A 10 min "normal" Ca(2+)-free pre-perfusion was sufficient to abolish the protective potency of the subsequent perfusion phase in the presence of the protective agent. The gap junction channel blocker heptanol (2 mmol/l) markedly decreased enzyme release during re-perfusion, but did not afford protection. Sarcosolic free cation concentrations were measured during Ca(2+)-free acidic perfusion. [Na+]i was markedly increased to about 44 mmol/l without predisposing to cell damage under these conditions. A marked reduction of cell damage was also afforded under conditions of hypoxia during Ca(2+)- and substrate-free perfusion. Acidosis (pHe = 6.5) under these conditions prevented a lethal increase of [Ca2+]i (2 mumol/l) and partially preserved a negative membrane potential. It is concluded that the predisposition to the Ca2+ paradox is produced by a permeabilisation of gap junction channels at low [Ca2+]e and that upon re-elevation of [Ca2+]e a serious Ca2+ influx proceeds through these leaks.
ATP delivery and its usage are achieved by cycling of respective intermediates through interconne... more ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill's equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca 2+ ]. Muscular fatigue is triggered when
The present paper concerns with ion homeostatic reactions in view of stimulus-secretion coupling ... more The present paper concerns with ion homeostatic reactions in view of stimulus-secretion coupling of the beta-cell, including Ca2+ fluxes of the endoplasmatic reticulum (ER). A steady state of cytosolic sodium and potassium ion concentrations ([Na+]c and [K+]c, respectively), and of the membrane potential (Delta c phi) can be attained only, if the flux through the electrogenic Na-K pump (JNaK) is balanced electrically, and if JNaK is rather high (about 25% of total ATP consumption at 10 mM glucose). Metabolically caused changes of cellular pH are unlikely, because, on the one hand, CO2 can rapidly leave the cell through cellular membranes, and because ATP cycling cannot produce nor consume protons. A slight decrease of pHc during cellular activity is caused mainly by an increased Ca-H exchange flux through the plasma membrane Ca2+ pump (J PMCA), which might be overcome, however, by H+ transport into secretory granules. The present simulations show that the conductance of ATP-sensitive K+ channels (K ATP) is highly susceptible to changes of [Mg2+]c. As a physical link between the Ca2+ filling state of the ER and the initiation of a depolarising, Ca2+ release-activated current (I CRAN), a metabolite (inositol 1,4,-diphosphate (IP2)) of the inositol 1,4,5-triphosphate (IP3) cycle is introduced. Sufficient ATP for insulin secretion is made available during glucose activation by [IP2] inhibition of a parallel [ATP]c consuming flux through protein biosynthesis (J Pbs). This leads to fast oscillations with a triphasic patterns of [Ca2+]c oscillations. Slow oscillations are initiated by including a Ca2+ leak current through highly uncoupled SERCA3 pumps. Both types of oscillations may superimpose yielding compound bursting and mixed oscillations of [Ca2+]c.
Book Publisher International (a part of SCIENCEDOMAIN International), Jul 23, 2021
A major goal of this study is to show how chemical and biochemical reactions occur. Since a large... more A major goal of this study is to show how chemical and biochemical reactions occur. Since a large part of the energy transformations occurring via a reaction is always related to changes in potential differences, these phenomenological events are initially also in the foreground. In addition to these energetic changes, however, entropic changes are also important. Here, special emphasis is placed on distinguishing between exchanged and produced entropy. The conversion of energy in chemical reactions into heat energy occupies a special position compared to the conversions of e.g. mechanical or electrical energy in that no forces are involved in the former. Using transport reactions through channels, the process can be expressed in a simplified form. It is made clear that heat generation occurs via energetic transition states, and that it is this generated heat itself that leads to a significant increase in multiplicity. As a result, the reaction process is allowed to take place. The conclusion is that in chemical and biochemical reactions, instead of a force, multiplicity determines the direction and course of such processes.
Rabbit erythrocytes were separated by centrifugation on a discontinuous Percoll gradient into fra... more Rabbit erythrocytes were separated by centrifugation on a discontinuous Percoll gradient into fractions of progressively increasing cell age to measure the in vivo decline in catalytic activity of eleven enzymes during the erythrocyte life span. Erythrocyte enzymes decline exponentially at different rates. The maximal and minimal catalytic activities (erythrocyte catalytic activity at the beginning and at the end of the erythrocyte life span), the intracellular half-life of enzymes and the daily loss of catalytic activity of total body erythrocytes were estimated.
Journal of Molecular and Cellular Cardiology, Jun 1, 1995
Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective... more Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective conditions against the Ca2+ paradox. In addition sarcosolic free cation concentrations and the membrane potential were measured employing ion-selective microelectrode techniques during Ca(2+)-free perfusion. Low temperature (18 degrees C), low pH (6.5 or 6.1), and polyethylene glycol (9%) during Ca(2+)-free perfusion all protected isolated hearts against the Ca2+ paradox. Protection could only be afforded if the protective agent was continuously present from the beginning of the Ca(2+)-free perfusion period. A 10 min "normal" Ca(2+)-free pre-perfusion was sufficient to abolish the protective potency of the subsequent perfusion phase in the presence of the protective agent. The gap junction channel blocker heptanol (2 mmol/l) markedly decreased enzyme release during re-perfusion, but did not afford protection. Sarcosolic free cation concentrations were measured during Ca(2+)-free acidic perfusion. [Na+]i was markedly increased to about 44 mmol/l without predisposing to cell damage under these conditions. A marked reduction of cell damage was also afforded under conditions of hypoxia during Ca(2+)- and substrate-free perfusion. Acidosis (pHe = 6.5) under these conditions prevented a lethal increase of [Ca2+]i (2 mumol/l) and partially preserved a negative membrane potential. It is concluded that the predisposition to the Ca2+ paradox is produced by a permeabilisation of gap junction channels at low [Ca2+]e and that upon re-elevation of [Ca2+]e a serious Ca2+ influx proceeds through these leaks.
In the present study, energetic and entropic changes are investigated on a comparative basis, as ... more In the present study, energetic and entropic changes are investigated on a comparative basis, as they occur in the volume changes of an ideal gas in the Carnot cycle and in the course of the chemical reaction in a lead-acid battery. Differences between reversible and irreversible processes have been worked out, in particular between reversibly exchanged entropy (e S ∆) and irreversibly produced entropy (i S ∆). In the partially irreversible case, e S ∆ and i S ∆ add up to the sum S ∆ for the volume changes of a gas, and only this function has an exact differential. In a chemical reaction, however, e S ∆ is independent on reversibility. It arises from the different intramolecular energy contents between products and reactants. Entropy production in a partially irreversible Carnot cycle is brought about through work-free expansions, whereas in the irreversible battery reaction entropy is produced via activated complexes, whereby a certain, variable fraction of the available chemical energy becomes transformed into electrical energy and the remaining fraction dissipated into heat. The irreversible reaction process via activated complexes has been explained phenomenologically. For a sufficiently high power output of coupled reactions, it is essential that the input energy is not completely reversibly transformed, but rather partially dissipated, because this can increase the process velocity and consequently its power output. A reduction of the counter potential is necessary for this purpose. This is not only important for man-made machines, but also for the viability of cells.
ATP delivery and its usage are achieved by cycling of respective intermediates through interconne... more ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill's equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca 2+ ]. Muscular fatigue is triggered when
A major goal of this study is to show how chemical and biochemical reactions occur. Since a large... more A major goal of this study is to show how chemical and biochemical reactions occur. Since a large part of the energy transformations occurring via a reaction is always related to changes in potential differences, these phenomenological events are initially also in the foreground. In addition to these energetic changes, however, entropic changes are also important. Here, special emphasis is placed on distinguishing between exchanged and produced entropy. The conversion of energy in chemical reactions into heat energy occupies a special position compared to the conversions of e.g. mechanical or electrical energy in that no forces are involved in the former. Using transport reactions through channels, the process can be expressed in a simplified form. It is made clear that heat generation occurs via energetic transition states, and that it is this generated heat itself that leads to a significant increase in multiplicity. As a result, the reaction process is allowed to take place. The conclusion is that in chemical and biochemical reactions, instead of a force, multiplicity determines the direction and course of such processes.
Journal of Molecular and Cellular Cardiology, Jun 1, 1995
Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective... more Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective conditions against the Ca2+ paradox. In addition sarcosolic free cation concentrations and the membrane potential were measured employing ion-selective microelectrode techniques during Ca(2+)-free perfusion. Low temperature (18 degrees C), low pH (6.5 or 6.1), and polyethylene glycol (9%) during Ca(2+)-free perfusion all protected isolated hearts against the Ca2+ paradox. Protection could only be afforded if the protective agent was continuously present from the beginning of the Ca(2+)-free perfusion period. A 10 min "normal" Ca(2+)-free pre-perfusion was sufficient to abolish the protective potency of the subsequent perfusion phase in the presence of the protective agent. The gap junction channel blocker heptanol (2 mmol/l) markedly decreased enzyme release during re-perfusion, but did not afford protection. Sarcosolic free cation concentrations were measured during Ca(2+)-free acidic perfusion. [Na+]i was markedly increased to about 44 mmol/l without predisposing to cell damage under these conditions. A marked reduction of cell damage was also afforded under conditions of hypoxia during Ca(2+)- and substrate-free perfusion. Acidosis (pHe = 6.5) under these conditions prevented a lethal increase of [Ca2+]i (2 mumol/l) and partially preserved a negative membrane potential. It is concluded that the predisposition to the Ca2+ paradox is produced by a permeabilisation of gap junction channels at low [Ca2+]e and that upon re-elevation of [Ca2+]e a serious Ca2+ influx proceeds through these leaks.
ATP delivery and its usage are achieved by cycling of respective intermediates through interconne... more ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill's equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca 2+ ]. Muscular fatigue is triggered when
The present paper concerns with ion homeostatic reactions in view of stimulus-secretion coupling ... more The present paper concerns with ion homeostatic reactions in view of stimulus-secretion coupling of the beta-cell, including Ca2+ fluxes of the endoplasmatic reticulum (ER). A steady state of cytosolic sodium and potassium ion concentrations ([Na+]c and [K+]c, respectively), and of the membrane potential (Delta c phi) can be attained only, if the flux through the electrogenic Na-K pump (JNaK) is balanced electrically, and if JNaK is rather high (about 25% of total ATP consumption at 10 mM glucose). Metabolically caused changes of cellular pH are unlikely, because, on the one hand, CO2 can rapidly leave the cell through cellular membranes, and because ATP cycling cannot produce nor consume protons. A slight decrease of pHc during cellular activity is caused mainly by an increased Ca-H exchange flux through the plasma membrane Ca2+ pump (J PMCA), which might be overcome, however, by H+ transport into secretory granules. The present simulations show that the conductance of ATP-sensitive K+ channels (K ATP) is highly susceptible to changes of [Mg2+]c. As a physical link between the Ca2+ filling state of the ER and the initiation of a depolarising, Ca2+ release-activated current (I CRAN), a metabolite (inositol 1,4,-diphosphate (IP2)) of the inositol 1,4,5-triphosphate (IP3) cycle is introduced. Sufficient ATP for insulin secretion is made available during glucose activation by [IP2] inhibition of a parallel [ATP]c consuming flux through protein biosynthesis (J Pbs). This leads to fast oscillations with a triphasic patterns of [Ca2+]c oscillations. Slow oscillations are initiated by including a Ca2+ leak current through highly uncoupled SERCA3 pumps. Both types of oscillations may superimpose yielding compound bursting and mixed oscillations of [Ca2+]c.
Book Publisher International (a part of SCIENCEDOMAIN International), Jul 23, 2021
A major goal of this study is to show how chemical and biochemical reactions occur. Since a large... more A major goal of this study is to show how chemical and biochemical reactions occur. Since a large part of the energy transformations occurring via a reaction is always related to changes in potential differences, these phenomenological events are initially also in the foreground. In addition to these energetic changes, however, entropic changes are also important. Here, special emphasis is placed on distinguishing between exchanged and produced entropy. The conversion of energy in chemical reactions into heat energy occupies a special position compared to the conversions of e.g. mechanical or electrical energy in that no forces are involved in the former. Using transport reactions through channels, the process can be expressed in a simplified form. It is made clear that heat generation occurs via energetic transition states, and that it is this generated heat itself that leads to a significant increase in multiplicity. As a result, the reaction process is allowed to take place. The conclusion is that in chemical and biochemical reactions, instead of a force, multiplicity determines the direction and course of such processes.
Rabbit erythrocytes were separated by centrifugation on a discontinuous Percoll gradient into fra... more Rabbit erythrocytes were separated by centrifugation on a discontinuous Percoll gradient into fractions of progressively increasing cell age to measure the in vivo decline in catalytic activity of eleven enzymes during the erythrocyte life span. Erythrocyte enzymes decline exponentially at different rates. The maximal and minimal catalytic activities (erythrocyte catalytic activity at the beginning and at the end of the erythrocyte life span), the intracellular half-life of enzymes and the daily loss of catalytic activity of total body erythrocytes were estimated.
Journal of Molecular and Cellular Cardiology, Jun 1, 1995
Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective... more Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective conditions against the Ca2+ paradox. In addition sarcosolic free cation concentrations and the membrane potential were measured employing ion-selective microelectrode techniques during Ca(2+)-free perfusion. Low temperature (18 degrees C), low pH (6.5 or 6.1), and polyethylene glycol (9%) during Ca(2+)-free perfusion all protected isolated hearts against the Ca2+ paradox. Protection could only be afforded if the protective agent was continuously present from the beginning of the Ca(2+)-free perfusion period. A 10 min "normal" Ca(2+)-free pre-perfusion was sufficient to abolish the protective potency of the subsequent perfusion phase in the presence of the protective agent. The gap junction channel blocker heptanol (2 mmol/l) markedly decreased enzyme release during re-perfusion, but did not afford protection. Sarcosolic free cation concentrations were measured during Ca(2+)-free acidic perfusion. [Na+]i was markedly increased to about 44 mmol/l without predisposing to cell damage under these conditions. A marked reduction of cell damage was also afforded under conditions of hypoxia during Ca(2+)- and substrate-free perfusion. Acidosis (pHe = 6.5) under these conditions prevented a lethal increase of [Ca2+]i (2 mumol/l) and partially preserved a negative membrane potential. It is concluded that the predisposition to the Ca2+ paradox is produced by a permeabilisation of gap junction channels at low [Ca2+]e and that upon re-elevation of [Ca2+]e a serious Ca2+ influx proceeds through these leaks.
Uploads