The control of sugar uptake by metabolic demand in isolated adult rat heart cells.

Abstract

SUMMARY. To investigate the control of sugar uptake by metabolic demand, we used isolated quiescent adult rat heart cells in suspension, under conditions similar to those found during anoxia. Metabolic demand was varied by exposing cells to rotenone plus various levels of ptrifluoromethoxyphenylhydrazone. Without glucose, the time taken for half of the cells to undergo contracture was inversely proportional to the metabolic demand as measured by the rate of lactate production. For any metabolic demand, the onset of contracture was preceded by a sudden drop in adenosine triphosphate. The permeability of contracted cells to glucose was investigated using 3-0-methylglucose. The rate of 3-0-methylglucose uptake by such cells was strongly dependent on the time taken for half the cells to undergo contracture, with low rates at low times to half contracture, and insulin-like rates at high times to half contracture. This suggests that the full induction of glucose transport by metabolic demand can be prematurely curtailed by the loss of adenosine triphosphate. This phenomenon appeared to limit glucose utilization in cells with a high metabolic demand when glucose was present: such cells underwent contracture unless insulin was also present, the rate of glucose uptake as measured with 2-deoxyglucose was inhibited, and the rate of lactate production was inhibited. Isoproterenol depressed glucose transport by two mechanisms. First, by stimulating the basal metabolic demand of the cell it reduced the time taken for half the cells to undergo contracture and, hence, the level of induced sugar transport. Second, it significantly delayed the onset of sugar permeability with respect to the contracture event. Consequently, cells treated with isoproterenol were more prone to contracture than cells without isoproterenol. (Circ Res 58: 157-165, 1986) EXPOSURE of whole isolated rat hearts to periods of anoxia results in activation of glucose transport (Morgan et al., 1959). The complexity of the whole heart has made it difficult to investigate in detail the way in which glucose uptake is controlled under these conditions. The recent advent of preparations of isolated adult heart cells that resist physiological levels of calcium has made it possible to investigate this question. In this study, anoxia was simulated by the addition of rotenone to inhibit mitochondrial respiration. Various amounts of p-trifluoromethoxyphenylhydrazone (FCCP) were added to achieve increased levels of metabolic demand. By 'metabolic demand,' we mean the rate of adenosine triphosphate (ATP) utilization by cells sustaining normal levels of ATP. For such cells, the metabolic demand is equal to the rate of ATP production. Normally, most ATP resynthesis would occur by oxidative phosphorylarion. In the presence of rotenone, ATP production is restricted to that from glycolysis, plus a transient and limited contribution from creatine phosphate. Indeed, since there is an obligatory link between glycolysis and ATP production, glycolysis cannot proceed unless there...

Anoxic contractile failure in rat heart myocytes is caused by failure of intracellular calcium release due to alteration of the action potential.

“…Alternatively, heterogeneity may be intercellular-the large outward conductance ofa few cells that are ATP depleted electrotonically shunting intact cells. This situation would be compatible with the large cell-tocell variability in lag duration that precedes contractile failure and with the heterogeneity in time of ATP depletion found in anaerobic cell suspensions (9). The latter studies showed that substantial ATP depletion precedes structural contracture by 1-6 min, similar to the time elapsing between contractile failure and contracture in our studies.…”

“…The mechanism of contractile failure has been difficult to study in multicellular preparations because of the effects of heterogeneity (8)(9)(10) and decreased cell-to-cell electrical coupling during hypoxia (11). To produce hypoxia in a single isolated cell, however, a Po2 as low as 0.15 torr (1 torr = 133 Pa) must be achieved (12).…”

Acute Modulation of Sugar Transport in Brain Capillary Endothelial Cell Cultures during Activation of the Metabolic Stress Pathway

“…Metabolic depletion rapidly stimulates sugar transport in these tissues (33)(34)(35). In this study, we demonstrate rapid depletion of ATP in bEnd.3 cells using metabolic poisons.…”

“…Previous studies have used the metabolic poisons KCN and FCCP to induce acute metabolic stress in cardiomyocytes, skeletal muscle, and nucleated erythrocytes (33)(34)(35). Metabolic depletion rapidly stimulates sugar transport in these tissues (33)(34)(35).…”

Control of the Na-Ca exchanger in isolated heart cells. I. Induction of Na-Na exchange in sodium-loaded cells by intracellular calcium.

“…The method is an extension of that previously used in our laboratory for measuring solute fluxes. [24][25][26] The new feature of the method is that concentrated cells are labeled with 22Na to a high specific activity and then diluted 10-fold into unlabeled medium before centrifugation. The dilution results in a 10-fold higher specific activity of 22Na inside the cell compared with 22Na outside and hence allows a 10-fold enhancement of the sensitivity of measurement of intracellular sodium compared with that of our basic method.…”