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Biomedical subjects

H M Piper

Publications and source records attributed to H M Piper.

At least 163 records · Page 9Linked to original sources
PubMed1985

The calcium and the oxygen paradox: non-existent on the cellular level.

Ca2+-tolerant isolated adult heart cells can be exposed to 1 mM EGTA and then again to 1 mM CaCl2 without developing irreversible hypercontracture. Thus, they are not subject to the calcium paradox, even though they apparently become more permeable to Na+ during Ca2+-free incubation. When these cells are incubated anoxically without substrate they slowly lose their energetic reserves. The process resembles that of the arrested anoxic myocardium. The appearance of irreversibly hypercontracted cells is neither accompanied by a parallel increase in enzyme release nor by an aggravation of the anoxia-induced damage by reoxygenation. Thus these cells are not subject to the oxygen paradox. It is suggested that the differences between the myocytes' behaviour in tissue and in the isolated state are due to the fact that the isolated cells are free from mechanical interactions with adjacent cells.

Adenosine Triphosphate↗
PubMed1985

Substrates for the attachment of adult cardiac myocytes in culture.

To achieve early cellular attachment of isolated adult cardiac myocytes in primary culture, various procedures were tested. A selective attachment of rod-shaped cells can be obtained either on serum-preincubated tissue-culture plastic dishes, or on modified plastic materials to which serum proteins are bound covalently, or on laminin. For the pretreatment of tissues culture dishes fetal calf serum is better suited than other sera.

Animals↗
PubMed1985

Adaptation phenomena of adult cardiac myocytes in culture.

Adult ventricular muscle cells attach firmly on serum pretreated tissue culture dishes during the first 3 hours of incubation. During one week of serum-free culturing in M-199 medium their ultrastructure changes only little, as opposed to their behaviour in a coculture with hepatocytes. In culture, adjacent myocytes develop new intercellular contacts some of which exhibit the morphological characteristics of nexus. During one week in the monoculture, spontaneous beating is not observed, but in the coculture system it is found after three days in flat, structurally transforming cells.

Adaptation, Physiological↗
PubMed1985

Oxygen demand of calcium-tolerant adult cardiac myocytes.

Isolated Ca2+-tolerant myocytes are mechanically at rest. Therefore, minimal oxygen demands should be expected. If oxygen consumption is measured without mechanical agitation of the cells, consumption rates comparable to those of the arrested myocardium are measured. In the current literature, much higher values are usually reported. It is suggested that these are due to mechanical stimulation of the cells in stirred suspensions.

Aging↗
PubMed1985

Temperature dependence of calcium antagonist action.

Calcium-tolerant ventricular myocytes from adult rats were electrically stimulated. The maximal contraction frequency (fm) was determined at different temperatures. In drug-free Tyrode solution, fm follows the Arrhenius equation from 7 to 39.5 degrees C. However, all investigated calcium antagonist drugs (verapamil, nifedipine, diltiazem, fendiline) introduce a discontinuity between 27 and 30 degrees C into the Arrhenius plots of fm. Above this transition temperature calcium antagonists lower fm more pronouncedly than below. Below, 10- or 100 fold higher concentrations are needed for the same relative effect as at 37 degrees C. It is argued that these findings might be important in cardiac surgery when calcium antagonists are used for cardioplegia at deep hypothermia.

Animals↗
PubMed1984

Relation between enzyme release and metabolic changes in reversible anoxic injury of myocardial cells.

Cultured adult cardiac myocytes were exposed to anoxia under substrate-free conditions. When compared to the metabolic changes in the oxygen deficient organ, those in the anoxic cell culture proceed in a similar, yet prolonged manner. Release of cytosolic enzymes starts with minor energetic disturbances and proceeds in close correlation to the actual ATP decay. Below 2 mumol ATP/gww, an increasing number of cells becomes irreversibly damaged, but above, 30 min reoxygenation leads to extensive recovery of the whole preparation. The results indicate that leakage of cytosolic enzymes during the early stage of anoxia is due to a gradual protein release from the individual cells, related to reversible membrane alterations.

Adenosine Triphosphate↗
PubMed1984

Absence of reoxygenation damage in isolated heart cells after anoxic injury.

Cultured adult cardiac myocytes were exposed to anoxia under substrate-free conditions and then reoxygenated. When comparing the oxygen deficient organ to the anoxic cell culture, we see that metabolic changes in the latter system proceed in a similar, yet prolonged manner, as in arrested hearts. Release of cytosolic enzymes starts with minor energetic disturbances and proceeds closely correlated to the actual ATP level. Below 2 mumol ATP/gww, an increasing number of cells becomes irreversibly damaged, above this level, 30 min reoxygenation leads to extensive recovery of the whole preparation. The results indicate that leakage of cytosolic enzymes during the early stage of anoxia is due to a gradual protein release from the individual cells and is related to reversible membrane alterations. Reoxygenation does not induce changes considered typical of the 'oxygen paradox'. Since mechanical cell-cell interactions are absent in this model, it is suggested that aggravation of tissue damage in heart tissue reoxygenated late is mainly caused by mechanical forces.

Adenosine Triphosphate↗
PubMed1984

Low resting potentials in single isolated heart cells due to membrane damage by the recording microelectrode.

Single myocytes from adult rat hearts were prepared following the method of Powell and co-workers (9, 10, 11). Low resting potentials (Em) could be improved by three techniques. (i) Elevation of Cao to 7.2 mM which, however, mostly resulted in spontaneity and irreversible contracture. (ii) Pre-incubation in a "KB medium" (6). (iii) Use of suction pipettes instead of tapered microelectrodes for intracellular recordings (2). It is concluded that low Em measured previously (11) were due to membrane damage upon microelectrode impalement accompanied by insufficient healing of the membrane around the electrode insertion.

Animals↗
PubMed1984

Energy metabolism and enzyme release of cultured adult rat heart muscle cells during anoxia.

An intact preparation of adult ventricular muscle cells was incubated in substrate-free, pH-constant, anoxic Tyrode solution. The time course of metabolic changes was found to depend on the relation of cell number to incubation volume: the smaller the volume, the faster anoxic damage develops. Energy needs decline rapidly during anoxia. Yet glycolytic energy production remains insufficient, since it also declines. Glycogenolysis stops after degradation of only half the glycogen present initially. Release of cytosolic enzymes (LDH, MDH) starts with the initial decrease in high-energy phosphates and proceeds correlated to the actual ATP content (r = -0.98) during the stage of reversible cell injury. An ATP content of 2 mumol/g wet wt. marks a critical threshold, below which more and more cells become irreversibly damaged. In the cell culture system, the anoxic process develops similarly to that of the oxygen deficient organ, however prolonged as in arrested hearts.

Adenine Nucleotides↗
PubMed1984

Kinetic analysis of myocardial fatty acid oxidation suggesting an albumin receptor mediated uptake process.

The relationship between extracellular albumin and non-esterified fatty acid (NEFA) concentrations and the rate of fatty acid oxidation was studied. The data were obtained from tests performed on a working rat heart. When NEFA concentration was increased the rate of fatty acid oxidation showed a saturation curve at a constant NEFA/albumin ratio. Keeping constant the albumin concentration, a rise in NEFA concentration resulted in a linear increase of fatty acid oxidation. No correlation, however, was found between fatty acid oxidation and the unbound fraction of fatty acids. These results suggest an albumin receptor mediated NEFA uptake. With this assumption the following rate law of the NEFA uptake was derived: UPT = UPT0 X [FA]/(Km + [ALB] ) where [FA] and [ALB] are the total NEFA- and albumin concentrations, UPT0 and Km are constants. The rates of oxidation computed with this equation show a very good congruence to the values obtained experimentally. The validity of the rate law is confirmed by the fact that it is shown to be in agreement to the results of other investigators.

Animals↗
PubMed1984

Temperature dependence of nifedipine action.

Recently, the use of calcium antagonists has been proposed as a new cardioplegic principle. At high doses (e.g. 10(-6)M nifedipine [3]) these drugs can be used for induction of reversible cardiac arrest. Apart from their effect on coronary flow, calcium antagonists seem to be beneficial to ischemic tissue because of their negative inotropic effect at high doses [6, 9]. Ionic cardioplegic solutions are commonly used in an advantageous combination with hypothermia. In the case of calcium antagonists, there is an indication that the specific cardioprotective effect is lessened at low temperatures [3]. Nifedipine is known to reduce contraction force without abolishing the generation of action potentials even at excessive doses [2]. To quantify the suppressing effect of nifedipine on the generation of contractions, we determined the maximal possible contraction frequency (Fm) under electrical stimulation at different temperatures. In isolated myocardial cells, Fm can be determined from the cell contour movements even with an almost complete force reduction and therefore it represents a measure for effective contractile refractoriness.

Animals↗
PubMed1984

Early enzyme release from myocardial cells is not due to irreversible cell damage.

It is often assumed that the release of enzymes from oxygen deficient heart tissue is due to the irreversible damage of myocardial cells. However, because of diffusion barriers and inhomogeneity of oxygen-deficient tissue this hypothesis cannot be proven in heart tissue. The question whether enzyme release may already occur during reversible injury is of considerable relevance in clinical medicine: first, because the amount of released enzyme activity has been used to estimate the mass of damaged tissue in cardiac infarction and, second, because the stress of some diagnostic interventions may lead to cardiac enzyme release, which according to the irreversibility hypothesis would indicate the death of cells in a cell constant organ.

Acid Phosphatase↗
PubMed1984

Inhibition of fatty acid oxidation and decrease of oxygen consumption of working rat heart by 4-bromocrotonic acid.

Nonesterified fatty acids (NEFA), glucose and lactate are major fuels for myocardial energy production. The ratio of energy produced and oxygen consumed, which can be expressed as ATP/O ratio, is different for each substrate: e.g. 3.17 for glucose and 2.83 for palmitate. Direct measurements, however, have shown that the difference of oxygen consumption is about twice as great as theoretically expected. This difference is of little significance under aerobic conditions, but may be important when oxygen supply is restricted. Numerous attempts have been made to reduce oxygen consumption by activating carbohydrate oxidation or inhibiting fatty acid metabolism. As the rate of fatty acid oxidation has been shown to depend on arterial concentrations of NEFA and albumin, this may be one point of control. Further approaches such as increasing the arterial levels of glucose, insulin and potassium, have been controversially discussed. As 4-bromocrotonic acid has been found to inhibit the fatty acid oxidation in isolated rat heart mitochondria [8], this might be an effective agent to save oxygen by reducing the rate of fatty acid oxidation in intact hearts.

Animals↗
PubMed1984

Ultrastructure of cultured adult myocardial cells during anoxia and reoxygenation.

Cultured heart cells from adult rats were exposed to anoxia in a substrate-free Tyrode's solution at constant pH. In this system the metabolic and the morphologic pattern can be investigated simultaneously. Anoxic changes develop gradually above 2 mumol adenosine triphosphate (ATP)/ gww . Morphometry reveals that the morphologic changes are closely related to the energetic state: creatine phosphate (CP) decay is accompanied by the loss of small mitochondrial matrix granules (r = 0.97). The fall of ATP is coincident with sarcomere shortening (r = 0.95) and, below 4 mumol/ gww , with mitochondrial swelling (r = -0.88). The number of lipid droplets correlates with the ATP level during anoxia and reoxygenation (r = -0.92). The early energetic depletion is accompanied by a moderate release of cytosolic enzymes and morphologic changes: the appearance of sarcolemmal microblebs and an increase in subsarcolemmal vesicles. Below an average ATP level of 2 mumol/ gww an increasing number of individual cells fail to recover when reoxygenated . However, that failure is accompanied neither by massive enzyme release nor by ultrastructural damage regarded as typical for the "oxygen paradox."

Animals↗
PubMed1983

Fatty acid-membrane interactions in isolated cardiac mitochondria and erythrocytes.

The effects of long-chain fatty acids on mitochondrial functions and red cell stability were studied. In albumin-containing incubation media, fatty acid distribution between the albumin-bound and the unbound fraction was estimated by calculation. When fatty acids are compared to one another on the basis of identical unbound concentrations, their effectiveness differs by orders of magnitude. Fatty acids stimulate mitochondrial basic oxygen consumption, thus lowering the respiratory control index, without changing the ATP/O ratio at lower concentrations. Lower concentrations increase Ca2+ uptake velocity, but decrease maximal Ca2+ storage capacity. The order of effectiveness of different fatty acids is the same for both oxidative phosphorylation and Ca2+ uptake. The influence of fatty acids on red cell stability in hypotonic media is similar to these effects both in concentration range and in order of effectiveness. The influence of fatty acids on red cell stability and their critical micellar concentrations were investigated because these are general characteristics of 'detergent-like' compounds. Critical micellar concentrations of the fatty acids in physiological salt buffers are, in general, at least 10-fold higher than the concentrations exhibiting membrane effects in vitro. Based on these findings it is suggested that, of the various concentrations reported in literature for myocardial non-esterified fatty acids, only the lowest values are physiologically possible.

Animals↗
PubMedDate not supplied

Fatty acids are not an important fuel for coronary microvascular endothelial cells.

The metabolism by coronary microvascular endothelial cells (CMEC) of the heart typical substrates palmitate and lactate was compared to that of glucose and glutamine. Confluent cultures of CMEC were used. Palmitate oxidation was saturable and independent of the exogenous albumin concentration. Palmitate, 300 microM, lactate, 1 mM, and glutamine, 0.5 mM, were oxidized to 35, 46, and 56 nmol CO2/h x mg protein. These oxidation rates were decreased by 80, 66, and 48% in presence of 5 mM glucose. The largest energy yield was obtained by glycolytic breakdown of glucose. Glucose, 5 mM, was degraded to lactate by 99%, and oxidized in the Krebs cycle by only 0.04%. 1% was catabolized via the hexose monophosphate pathway. The rate of glucose oxidation in the Krebs cycle could be 30-fold increased by the uncoupler 2,4-dinitrophenol, 30 microM. At concentrations lower than 1 mM the amount of glucose oxidized in the Krebs cycle also grew, indicating existence of the Crabtree effect. The energy demand of CMEC seems to be of the same order as that of the arrested heart.

Animals↗
PubMedDate not supplied

Hypertrophic responsiveness to beta 2-adrenoceptor stimulation on adult ventricular cardiomyocytes.

The aim of the present study was to characterize the receptor subtype and the second messenger involved in the newly discovered hypertrophic effect of beta-adrenoceptor stimulation in cultures of adult ventricular cardiomyocytes. Cardiomyocytes isolated from adult rats and cultured for 6 days in presence of 20% fetal calf serum (FCS) were used as experimental model. Hypertrophic responsiveness of cardiomyocytes was characterized by rate of protein synthesis, increase in protein mass, and increase in RNA content. The hypertrophic effect of the non-specific beta-adrenoceptor agonist isoprenaline was abolished in presence of a specific beta 2-adrenoceptor antagonist (ICI 118,551), could be mimicked by use of a beta 2-adrenoceptor agonist (procaterol) or direct stimulation of adenylate cyclase (forskolin) or addition of a cell-permeable analogue of cAMP (dibuytyrylcyclo-AMP). In presence of Rp-cAMPS, an inhibitor of protein kinase A, the hypertrophic effect of isoprenaline was abolished. The results indicate that the hypertrophic effect of beta-adrenoceptor stimulation is due to stimulation of beta 2-adrenoceptors and activation of adenylate cyclase and protein kinase A.

Adenylyl Cyclases↗