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Biomedical subjects

H M Piper

Publications and source records attributed to H M Piper.

At least 145 records · Page 8Linked to original sources
PubMed1987

Coronary and myocardial adenosine receptors.

In the isolated guinea pig heart the rank oder of potency for coronary vasodilation is NECA greater than R-PIA greater than adenosine greater than S-PIA and this is characteristic for A2-adenosine receptors. Release of 3H-cyclic AMP from coronary endothelium in 3H-adenosine prelabeled hearts was augmented by these adenosine derivatives and followed the same rank order of potency. This identifies the coronary endothelial adenosine receptor to be of the A2-subtype. Similar results were obtained in bovine aortic endothelium in culture grown on microcarrier beads. Studies on isolated cardiac myocytes revealed, that adenosine derivatives did not alter basal cyclic AMP levels but attenuated the isoproterenol elicited increase, R-PIA being more potent than NECA. Thus, on cardiomyocytes the A1-adenosine receptor predominates and may be responsible for the antiadrenergic action of adenosine. Since vascular and cardiomyocyte adenosine receptors are of different subtypes this may be used as a specific marker to identify the origin of surface membranes prepared from cardiac tissue.

Adenosine↗
PubMed1987

Oxidative metabolism of cultured adult cardiomyocytes.

Cultured adult cardiomyocytes from rat exhibit, if unstimulated, low rates of substrate oxidation, corresponding to their mechanical inactivity. They oxidize exogenous fatty acids and lactate preferentially to glucose. Endogenous lipolysis provides the largest portion of oxidative substrates. Pyruvate dehydrogenase is largely in its inactive form. If glucose is the sole exogenous substrate, the quiescent cells produce lactate as a purely aerobic phenomenon probably reflecting the reduced state of the cytosol at low respiration rates.

Animals↗
PubMed1986

Importance of endogenous substrates for cultured adult rat cardiac myocytes.

In Ca-tolerant adult cardiomyocytes the contribution of endogenous substrates (glycogen, tri- and diacylglycerol) to oxidative substrate metabolism was investigated. After 4 h in culture medium (M 199 plus 4% fetal calf serum) the cellular triacylglycerol content is 3.6-fold higher than in fresh myocardium and reflects the free fatty acid composition of the medium. When triacylglycerol is degraded, all long-chain fatty acids are hydrolysed at equal rates. In these quiescent cells, the activity of pyruvate dehydrogenase is low (10% of full activity, in Tyrode solution with 5 mM glucose). Up to 30% of full pyruvate dehydrogenase activity, the contribution of non-lipid substrates (glycogen, glucose, lactate and pyruvate) to oxidative energy production is correlated to pyruvate dehydrogenase activity. At 5 mM medium concentration, glucose, lactate and pyruvate share in energy production the proportions of 15, 36 and 50%, whereas endogenous lipolysis accounts for 78, 61 and 46%. It is concluded that these quiescent cardiomyocytes represent cardiac metabolism in a basal state in which the preference for fatty acids, especially from endogenous lipids, is very pronounced. The utilization of endogenous substrates therefore has to be considered in all studies investigating the oxidative metabolism of these isolated cells.

Animals↗
PubMed1986

Calcium-shifts in anoxic cardiac myocytes. A cytochemical study.

Cultivated heart muscle cells from adult rats were exposed to anoxia in a substrate-free Tyrode solution at constant pH. It has been shown previously that in this system anoxic changes of metabolism and morphology develop gradually during the first 60 min. In this study, intracellular Ca2+ localization was pursued cytochemically. Under aerobic control conditions, Ca2+-deposits are only detected along the sarcolemma and T-tubules. Under anoxia the pattern changes gradually. During the first 60 min, the number of sarcolemmal deposits is transiently increased and single deposits appear inside mitochondria. After 90 and 120 min of anoxia, an increasing number of cells have lost their ability of sarcolemmal Ca2+ binding, but exhibit clustered deposits in single mitochondria. These cells are hypercontracted, often contain condensed myofibrillar masses and are covered with large sarcolemmal protrusions, indicating that they are irreversible injured. Loss of sarcolemmal Ca2+ binding ability seems to be a crucial event on the edge of the development of irreversible injury. Since the sarcolemmal Ca2+-deposits in normal cells are believed to be causally related to a binding of Ca2+ to anionic phospholipids, a decrease of Ca2+ affinity of these phospholipids and a change in the sarcolemmal phospholipid composition may be considered as causes for the disappearance of sarcolemma-bound Ca2+.

Animals↗
PubMed1986

Carbohydrate and fatty acid metabolism of cultured adult cardiac myocytes.

The energy metabolism of exogenous and endogenous substrates was investigated in Ca-tolerant adult ventricular myocytes in short-term culture. CO2 production from exogenous glucose (5 mM), lactate (5 mM), and palmitate (100 microM) were 8, 20, and 29 mumol X h-1 X g wet wt-1. Endogenous lipolysis shared in energy production by 78, 61, and 31%, respectively. Fatty acids represented the main respiratory fuel even when 10(-7) M insulin, 5 mM lactate, or 5 mM dichloroacetate were supplied in addition to glucose. With palmitate, triglyceride contents were doubled within 3 h of cell incubation. With 5 mM glucose as sole exogenous substrate the energy turnover in these resting cells resembled that of arrested hearts, corresponding to 2 ml O2 X min-1 X 100 g wet wt-1. It is concluded that the basic features of substrate metabolism resemble those of the intact myocardium in that fatty acids represent the major fuel, but the contribution of endogenous lipolysis is greater than in the beating heart.

Animals↗
PubMed1985

Development of new intercellular contacts between adult cardiac myocytes in culture.

On serum precoated tissue culture dishes, isolated ventricular myocytes attach firmly during 4 hours of incubation. Since in this monoculture cells do not divide and show only minimal signs of cytoplasmic spreading, individual cells mostly lie isolated from others. However, when occasionally two cells attach in close vicinity, new cell-cell contact structures are formed already during the first hours in culture. The de-novo formation of these communications is demonstrated by the finding that they often connect cells in an end-to-side manner that does not occur in vivo.

Animals↗
PubMed1985

Morphological dedifferentiation of adult cardiac myocytes in coculture with hepatocytes.

When adult heart cells are plated on a dish covered with a monolayer of hepatocytes gradual morphological changes are observed. While during the first day the myofibrils are still organized in rod-like shape, later the cells become flat and spread on top of underlying hepatocytes. After two days most cells have a flat, polygonal appearance with spread myofibrillar bundles. At this stage they start spontaneous rhythmic contractions which are characteristic for embryonic myocytes, but not for isolated adult ventricular cells. In this culture myocytes form specific contact structures to adjacent myocytes as well as to hepatocytes. These results demonstrate the phenotypical plasticity of adult heart muscle cells which are believed to be terminally differentiated.

Animals↗
PubMed1985

Temperature dependence of verapamil action.

Ca2+-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, verapamil introduces a discontinuity around 27 degrees C into the Arrhenius plot of fm. Above this transition temperature the calcium antagonist lowers fm more pronouncedly than below. Below, a tenfold higher concentration is needed for the same relative effect as at 37 degrees C. It is argued that this finding might be important in cardiac surgery when calcium antagonists are used for cardioplegia at deep hypothermia.

Animals↗
PubMed1985

Enzyme release and glycolytic energy production.

In substrate-free anoxia, activities of released cytosolic enzymes (LDH, MDH) correlate inversely with the actual ATP level (for both: r = -0.98). At the same time there is a close correlation between lactate production from glycogen and the ATP content (r = 0.98). With external glucose present enzyme release is greatly delayed, but this could be due to the stimulation of glycolysis as well as to the maintenance of high ATP levels. When glycolysis is blocked by iodoacetate under aerobic conditions, the cells also become depleted of high-energy phosphates. This depletion is delayed in the presence of pyruvate. Cytosolic enzyme release again is correlated with total ATP contents, by the same relation in the presence or absence of pyruvate. Glycolytic energy production is negligible in both cases and does not seem to determine enzyme release directly.

Acid Phosphatase↗
PubMed1985

Anoxia influences the lateral diffusion of a lipid probe in the plasma membrane of isolated cardiac myocytes.

Using the technique of fluorescence photobleaching recovery we have measured the characteristics of lateral diffusion of oleylaminofluorescein (OAF) in the plasma membrane of isolated rat cardiac myocytes under normoxic and anoxic conditions. The normoxic pattern is one of slow diffusion and low recovery (D = 1.8 +/- 0.3 X 10(-10)cm2/s, r = 0.44 +/- 0.059), while under anoxic conditions faster diffusion and higher recovery (D = 2.5 +/- 0.4 X 10(-9)cm2/s, r = 0.58 +/- 0.063) are observed, the change proceeding via an intermediate stage with a yet faster diffusing species (D greater than 2.5 X 10(-9)cm2/s). The process is reversible. We hypothesize that under normoxic conditions the lateral diffusion of OAF is hindered by the division of the cell membrane into a patchwork of more or less isolated domains by lateral and longitudinal barriers of spectrin (7, 13) which are rearranged under anoxic conditions to another pattern which permits the label greater, but still not unrestricted, freedom of movement.

Amines↗
PubMed1985

Anoxic injury of adult cardiac myocytes.

Cultured adult cardiocytes were exposed to anoxia. The initial decrease of high-energy phosphates was accompanied by a moderate release of cytosolic enzymes and morphological changes: the appearance of sarcolemmal 'microblebs' (approximately 1 micron in diameter) and an increase of subsarcolemmal vesicles. At ATP levels above 2 mumol/gww, metabolic and morphological alterations were reversible. Probably the sarcolemmal changes are causally related to the loss of macromolecules from reversibly injured cells. At ATP levels below 2 mumol/gww, an increasing number of cells become irreversibly hypercontracted. In these cells cytoplasmic masses are protruded into large 'macroblebs' (10-30 micron in diameter), however sarcolemmal continuity is preserved. Thus, enzyme release, irreversible contracture and cytolysis do not occur simultaneously in anoxic isolated cardiocytes.

Adenosine Triphosphate↗
PubMed1985

Substrate utilization of adult cardiac myocytes.

Cultured adult myocytes are in a state of basal metabolism. When glucose is the only exogenous substrate, they produce lactate over CO2 at a constant rate of 2.7 from this substrate. Increase of oxygen tension does not change this behaviour. Insulin preferentially increases lactate formation, dichloroacetate only CO2 production. The fact that the lactate/CO2 ratio can be varied from 0.5 to 16 indicates that there is no close coupling between glycolytic flux and pyruvate oxidation. Both exogenous lactate and fatty acids are used preferentially over glucose. But increase of fatty acid oxidation and inhibition of glucose oxidation are not complementary. Glycolytic flux is only slightly decreased when fatty acid oxidation is already saturated. The results indicate that fatty acids interact with glucose oxidation primarily by inactivation of the pyruvate dehydrogenase. Neither insulin nor dichloroacetate in the presence of glucose inhibit fatty acid oxidation.

Animals↗
PubMed1985

Single voltage-dependent and outward rectifying K+-channels in isolated rat heart cells.

Studies on single K+-channel currents recorded from isolated rat heart muscle cells, in which early repolarization is known to be exceptionally fast, are reported here. A K+-channel which is blocked by TEA (tetraethylammonium) from the inside only has been found. The total open time of the channel, measured in steady-state after activation, indicated outward rectifying properties. The single channel conductance increases with depolarization from 25 pS at -70 mV to 75 pS at + 70 mV. Selectivity of the channel has also been measured and it was found that only Rb+ and K+ can permeate the channel, whereas the permeability (P) for Li+, Na+, Cl-, Mg2+, and Ca2+ is less than 0.05 times PK+. Ba2+ and CS+ block the channel activity. These results clearly demonstrate the existence of K+-selective outward rectifying conductance pathways in rat ventricular myocytes.

Animals↗
PubMed1985

Development of ischemia-induced damage in defined mitochondrial subpopulations.

Two mitochondrial subpopulations were isolated from guinea-pig heart by density gradient centrifugation. Under control conditions, both contain functionally intact mitochondria in which ischemic damage develops similarly. However, in one subpopulation adenine nucleotide content, adenine nucleotide translocase activity, oxidative phosphorylation and Ca2+ uptake are a quarter lower than in the other one when related to mitochondrial protein mass. Cytochrome contents and uncoupled electron flux are the same. Changes develop most evidently at the very beginning of ischemia for NAD-linked respiration. When ischemia progresses, cytochromes and the translocator protein are gradually lost or inactivated. Thereupon only partial recovery of mitochondrial function can be obtained after 20 min of reperfusion.

Adenine Nucleotides↗
PubMed1985

Effect of fatty acid oxidation on efficiency of energy production in rat heart.

Myocardial fatty acid oxidation has been reported to be accompanied by an elevated O2 consumption compared with carbohydrate oxidation. The exact amount of this additional O2 consumption is controversial. Different investigators have observed an O2 wasting effect that is too large to be explained by the different ATP-to-O2 ratios of these substrates. With the use of isolated perfused rat hearts, O2 consumption and hemodynamic measurements were computer analyzed to provide on-line estimates of the ratio between O2 consumption and demand (EQ). Increasing palmitate or octanoate concentrations decreased the respiratory quotient, which was accompanied by a disproportionate increase of EQ. Inhibition of fatty acid oxidation by an inhibitor of acylcarnitine transferase or a blockade of mitochondrial thiolase caused a drastic reduction of fatty acid oxidation. The fatty acid-induced enhancement of O2 consumption was decreased to a much smaller extent, indicating that there are two different mechanisms responsible for the O2-wasting effect, one that depends on mitochondrial fatty acid oxidation and another that is not affected by an inhibition of this pathway.

Animals↗
PubMed1985

An index for estimation of oxygen consumption in rat heart by hemodynamic parameters.

To find a suitable index for the estimation of O2 consumption of rat hearts by use of hemodynamic parameters, isolated hearts were perfused under different working conditions. Coronary flow, arteriovenous O2 difference, cardiac output, and ventricular pressure curve were recorded and continuously fed into a computer. O2 consumption and different hemodynamic parameters such as dP/dtmax, maximum ventricular pressure, pressure-time integral, and heart rate were computed on-line. With the use of these data of 64 different steady states, numerous formulas containing hemodynamic parameters were tested with respect to their ability to predict O2 consumption. The best fit of the data was obtained by a linear combination of the products of rate times dP/dtmax and rate times pressure-time integral of one beat (r = 0.993). Indexes containing approximations of wall stress were not found to improve the predictive ability.

Animals↗
PubMed1985

Glucose, lactate, and palmitate as substrates for the resting cardiac myocyte.

Cultured adult cardiac myocytes oxidize fatty acids and lactate preferentially to glucose. In contrast to other results obtained with isolated cardiac myocytes the preference for fatty acids is not dependent on carnitine administration, suggesting that the cells of this preparation possess sufficient reserves of carnitine and an intact mechanism for fatty acid activation. It is demonstrated by the substrate oxidation rates that these quiescent cells are in a state of minimal metabolic demand, thus resembling the arrested myocardium.

Animals↗