Biomedical subjects

F Diederichs

Publications and source records attributed to F Diederichs.

10 recordsLinked to original sources

PubMed1997

A decrease of both [Ca2+]e and [H+]e produces cell damage in the perfused rat heart.

Cell damage of the Langendorff-perfused rat heart in response to a decrease of both [Ca2+]e and [H+]e is described. At pHe = 7.7, lactate dehydrogenase (LDH) release could be induced during perfusion with media of reduced [Ca2+]e (0.1-0.4 mmol/l). Decreasing pHe to normal abolished LDH release. The gap junction channel blocker heptanol (2 mmol/l) also reduced enzyme release, and polyethylene glycol (9% PEG6000) totally prevented cell damage. Elevation of buffer capacity of perfusion media or perfusion flow both increased LDH release. Cell damage could also be aggravated by substituting 10 mmol/l of [Na+]e by foreign cations. At [Ca2+]e = 0.1 mmol/l and pHe = 7.7, [Ca2+]i and [Na+]i of non-lysed cells were markedly increased (in HCO3/CO2 buffered media to about 7.0 micromol/l and 36 mmol/l, respectively; in HEPES-buffered media, to about 5.0 micromol/l and 55 mmol/l; physiological values of [Ca2+]i and [Na+]i are around 0.1 micromol/l and 10 mmol/l, respectively), whereas pHi was not appreciably elevated. In contrast to myocytes in the intact heart, [Ca2+]i of isolated cardiomyocytes under similar conditions was decreased to about 75 nmol/l and LDH release was negligible; pHi of isolated cardiomyocytes, as in intact myocardium, did not change appreciably. The results indicate that Ca2+ overload is produced at lowered [Ca2+]e and [H+]e by an influx of Ca2+ through gap junctional leaks.

Animals↗

PubMed1995

Protection of isolated rat heart against the Ca2+ paradox. Are gap junction channels involved?

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.

Alcohols↗

PubMed1994

Intracellular free Ca2+, Na+, and H+ concentrations in the isolated perfused rat heart during the Ca2+ paradox.

Enzyme release from the normothermic perfused rat heart was determined to evaluate myocardial cell damage during the perfusion sequence of the Ca2+ Ca2+ paradox. In addition sarcosolic free Ca2+ and monovalent cation concentrations were measured using ion-selective microelectrodes (ISMEs). A reduction of the extracellular Ca2+ concentration, [Ca2+]e, from 1.0 mmol/l to 0.3 or 0.1 mmol/l, respectively, during the re-perfusion period markedly decreased the rate of enzyme release. Slow Ca2+ channel blockers were less (verapamil) or not at all (nifedipine) effective in providing protection. The sarcosolic free Ca2+ and Na+ concentrations, [Ca2+]i and [Na+]i, were significantly (P < 0.01) elevated during Ca(2+)-free perfusion, [H+]i was not significantly changed, while the membrane potential became continuously more positive. Addition of verapamil to the perfusion medium increased [Na+]i, but did not further increase [Ca2+]i. The critical [Ca2+]i for cell damage was between 12 and 18 mumol/l. It could be demonstrated, that Ca2+ entry during re-perfusion via Na/Ca exchange is thermodynamically unlikely to elevate [Ca2+]i to critical values. It is concluded therefore that the predisposition of the rat heart for the Ca2+ paradox is brought about by membrane leaks, which form during Ca(2+)-free perfusion and that Ca2+ influx into the sarcosol proceeds mainly through these leaks.

Animals↗

PubMed1990

Myocardial cell damage and breakdown of cation homeostasis during conditions of ischaemia and reperfusion, the oxygen paradox, and reduced extracellular calcium.

Enzyme release from perfused rat heart was determined under various conditions of injury. In analogous experiments, intracellular cation concentrations were measured using ion-selective microelectrodes. Under appropriate conditions, the inhibition of mitochondrial and/or glycolytic ATP production led to a decrease in the release of enzymes. During ischaemia or the oxygen paradox, the sarcosolic Ca2+ concentration was highly elevated; reperfusion or reoxygenation was followed by a drastic enzyme release. This was also found to be true under the conditions of an increased permeability brought about by a reduced extracellular Ca2+ concentration of 0.1 mmol/l. The intracellular pH under all conditions of injury was only moderately decreased. The sarcosolic Na+ concentration was markedly increased whereas the K+ concentration was decreased. The critical Ca2+ concentration of the sarcosol beyond which cell damage and enzyme release are inducible was assumed to be in the range between 10 and 32 mumol/l. The driving force of the Na+/Ca2+ exchange reaction of the sarcolemma is discussed in relation to recovery from hypoxic injury and the potential for avoiding cell damage.

Adenosine Triphosphate↗

PubMed1986

Enzyme release from the perfused rat heart. The functions of the cytoskeleton under cell-pathological conditions.

The mechanism of enzyme release from Langendorff-perfused rat hearts was studied under the injury conditions of the Ca2+ paradox and 2,4-dinitrophenol poisoning. During perfusion with Krebs-Ringer buffer or in buffered sucrose sarcoplasmic enzymes were massively released when Ca2+ was reintroduced to the perfusion medium (Ca2+ paradox). Mitochondrial matrix enzymes were released to a very small extent. Only the cytoplasmic isoenzyme of the bilocular enzyme malate dehydrogenase was released. The release kinetics of various enzymes with greatly differing molecular weights showed no significant differences. Qualitatively the same results were obtained under 2,4-dinitrophenol poisoned conditions in Ca2+ -free sucrose media. Sarcoplasmic enzymes were massively released, mitochondrial enzymes did not appear in the perfusate. 2,4-Dinitrophenol poisoning alone was not sufficient to cause enzyme release. An additional swelling under these conditions was necessary. ATP from the extracellular space was able to enhance the enzyme release, which was brought about by 2,4-dinitrophenol and cell swelling. A hypothesis is presented that enzyme release is produced by initiating a membrane blebbing process. An elevated intracellular Ca2+ concentration is a necessary prerequisite. In the presence of ATP, active membrane blebbing is caused by contractions of the membrane-anchored cytoskeleton. In the absence of ATP passive membrane blebbing is induced by cell swelling, provided that the cytoskeleton has been crosslinked by Ca2+.

2,4-Dinitrophenol↗

PubMed1986

The decline of catalytic enzyme activity concentration of in vivo ageing erythrocytes of the man, the dog and the rat. Approach to a quantitative diagnostic enzymology, IV. Communication.

Human, dog and rat erythrocytes were separated by centrifugation on a discontinuous buffered Percoll gradient into fractions of progressively increasing mean cell age to measure the in vivo decline in catalytic activity of eleven enzymes during the erythrocyte lifespan. Erythrocyte enzymes decline exponentially at different rates and also differ between the species. The maximal and minimal catalytic activities (erythrocyte catalytic activity at the beginning and at the end of the appropriate erythrocyte life-span for a given species) and the intracellular half-life of enzymes estimated. To test the hypothesis that circulating erythrocytes make a significant contribution to the normal catalytic activity in plasma it was assumed as a working hypothesis that the measured loss of catalytic activity in ageing erythrocytes is equivalent to the amount of the enzymes released in catalytically active form into plasma. This contribution was calculated.

Adult↗

PubMed1986

Kinetic of adjustment of enzyme catalytic concentrations in the extracellular space of the man, the dog and the rat. Approach to a quantitative diagnostic enzymology, V. Communication.

The high degree of constancy of enzyme catalytic activity in the plasma of a given individual is regulated by a complex system of flux equilibria consisting of eight basic processes. Some of these processes are of primarily theoretic importance. Enzymes from all tissues of the body, including the liver, are released via a continuous physiological process into the interstitial space and get into the intravascular space by way of lymphatic transport. The release of enzymes from tissues directly into the intravascular space is of secondary importance as is the exchange of enzyme molecules across capillary membranes from the intravascular to the interstitial space and vice versa. In contrast, enzymes from circulating blood cells are transported directly into the intravascular space. Enzymes are removed from the intravascular space at rates which vary greatly between both enzymes and species. In a review of the literature, half-lives of diagnostically important enzymes in plasma of man, dogs and rats were given and the striking differences in the results for a given enzyme are discussed from a methodological point of view. In a mathematical analysis, data for lymphatic transport of enzymes from dogs and rats (Lindena et al. (1986) this J. 24, 19-33) and of enzyme efflux from in vivo ageing erythrocytes (Lindena et al. (1986) this J. 24, 49-59) into the plasma are related to the elimination rate constants of enzymes from the plasma. The contribution of lymphatically transported enzymes to the basal catalytic activity in plasma (Lindena & Trautschold (1986) this J. 24, 11-18) amounts to 55-80% for lactate dehydrogenase and malate dehydrogenase, 80-90% for adenylate kinase and phosphohexose isomerase, 90-95% for aspartate aminotransferase and aldolase and 99% for creatine kinase. A model of Ca2+ -mediated vesicular transport of enzymes out of ageing erythrocytes is proposed. The importance of lymphatically transported enzymes to total plasma catalytic activity in dogs and rats argues for a similar contribution of lymph transport in man.

Animals↗

PubMed1986

Intracellular free Ca2+ in the course of the Ca2+ paradox and during poisoning. Ca2+-selective microelectrode measurements in the perfused rat heart.

The free intracellular Ca2+ concentration of perfused rat hearts was measured using Ca2+-selective microelectrodes. In Krebs-Ringer bicarbonate buffer + 0.1 mmol/l Ca2+ (controls) the intracellular Ca2+ concentration was 0.87 +/- 0.07 mumol/l and the membrane potential was -51.5 +/- 0.3 mV. Without glucose the membrane potential approached zero after ca. 60 min, whereas the Ca2+ concentration during 110 min increased only slowly to 10.0 mumol/l. During Ca2+-free perfusion (5 min) both parameters did not change significantly. With reintroduction of 2.0 mmol/l Ca2+ the membrane potential rapidly collapsed and the intracellular Ca2+ concentration was elevated above 0.1 mmol/l within two min. Reperfusion with only 0.1 mmol/l Ca2+ decelerated both changes. Poisoning by carbonyl cyanide-p-trifluoromethoxyphenylhydrazone or antimycin A in Ca2+-free Krebs-Ringer bicarbonate buffer increased the intracellular Ca2+ concentration to 30.0 and 25.0 mumol/l, and the membrane potential was collapsed after 16 and 10 min, respectively. In antimycin A- and Ca2+-containing sucrose medium the intracellular Ca2+ during 16 min increased above 1.0 mmol/l, and the membrane potential began to increase only after 10 min. The results are consistent with the postulate of a hypothetical mechanism of cell injury, in which noxious membrane-cytoskeleton interactions are induced by an elevated intracellular Ca2+ concentration. It is concluded that Ca2+ entry via Na/Ca exchange is not fundamentally involved with induction of injury.

Animals↗

PubMed1985

The decline in catalytic enzyme activity concentration with aging of the rabbit erythrocyte.

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.

Animals↗

PubMed1979

On the mechanism of lactate dehydrogenase release from skeletal muscle in relation to the control of cell volume.

The mechanism of enzyme release from isolated skeletal muscle was illustrated by the study of the release of lactate dehydrogenase (LDH). In hypotonic media of different composition but of same tonicity the increase of LDH permeability was triggered at the same range of relative osmolality R (0.45 less than R less than 0.55), although the swelling in the respective media showed appreciable differences. The kinetics of muscle swelling showed that a deviation from the theoretically computed swelling curve to lower values of swelling was connected with an increased LDH permeability. The reduction of swelling was ATP- and Ca2+ and/or Mg2-dependent. It is concluded that swelling of cells generally precedes the leakage of soluble enzymes, and the cross-linking of filaments at the sarcoplasmic side of the sarcolemma under appropriate conditions can counteract swelling, thereby blebbing off the cell membrane from the filament meshwork. In the course of this process, sufficiently large membrane lesions are produced through which macromolecules may escape into the extracellular space.

Adenosine Triphosphate↗