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The role of ATP in energy deprivation contracture in unloaded rat ventricular myocytes
J Mol
Cell
Cardiol20
(Supplement
IV) (1988)
P-%THE
EFFECT OF METABOLIC SUBSTRATES ON INTRACELLULAR pi (PHI) DURING HYPOXIA IN QUIESENT SHEEP HEART PURKINJE FIBRES. C.M. Bright and D. Ellis. Department of Physiology, University Medical School, Teviot Place, Edinburgh, EH8 9AG. When oxidative phosphorylation is blocked by hypoxia there is an intracellular acidification which is followed on reoxygenation by a further transient acidification before recovery (Ellis & Noireaud, 1987. J. Physiol.382, 125-141). Cardiac tissue can utilize different metabolic substrates so the effects of glucose, pyruvate or acetate (20mM) during hypoxia were investigated. 30 minutes exposure to the substrate was followed by 20 minutes of hypoxia. In 6 experiments there appeared to be no significant difference (P>O.l in a 2 sample ttest) between hypoxia induced acidification in 20mM glucose, acetate or pyruvate compared to that in normal Tyrode (10mM glucose). This lack of significance could have been due to the wide variation in the effects of the various substrates. It is possible that the large glycogen stores of Purkinje fibres prevent the different effects of the substrates from being apparent in these relatively short term exposures. (Supported by the British Heart Foundation).
P-56
METABOLISM AND ACTION POTENTIAL SHORTENING $lJRING METABOLIC BLOCKADE AND ISCHAEMIA IN ISOLATED FERREI HEARTS. A.C. Elliott+ G.L. Smith+, D.G. Alleg+. 'Dept. of Physiology, University College London, LoAdon WClE 6BT, U.K. and Department of Physiological Sciences, University of Manchester, Manchester Ml3 9PT, U.K. Shortening of the action potential during ischaemia and metabolic blockade (inhibition of both aerobic and anaerobic metabolism) may contribute to the contractile failure which occurs under such conditions. It has been hypothesised that a decline in ATP causes the action potential shortening via the activation of ATP-sensitive Kt channels. We have measured ATP (with P-31 NMR) and action potential duration (using a suction electrode) simultaneously in isolated ferret hearts. Metabolic blockade caused a rapid fall in both contractility and action potential duration. ATP fell only slightly, and remained well above the range where activation of the ATP-sensitive I(+ channel would be expected to occur. This suggests that channel activation does not occur simply via a large fall in bulk ATP. In ischaemic hearts, we observed no fall in ATP and little action potential shortening during the development of contractile failure; taken together with other work (Eisner et al, J. Phvsiol. 390: 57P: 1987), this suggests that metabolic changes (intracellular acidosis and accumulation of inorganic phosphate) are largely responsible for contractile failure in ischaemic ferret hearts. Supported by the British Heart Foundation.
P- ,57
THE ROLE OF ATP IN ENERGY DEPRIVATION CONTRACTURE IN UNLOADED RAT VENTRICULAR MYOCYTES . C.G. Nichols & W.J. Lederer. Dept. of Physiology, Univ. Maryland School of Medicine, Baltimore, MD 21201, USA. Inhibition of high-energy phosphate production leads to the development of a contracture in ventricular muscle. Two potential mechanisms are: (1) a rise in intracellular [Ca*] (Cai); (2) a fall in intracellular [ATP] (ATPi) leading to formation of rigor bridges. In unloaded rat ventricular cells, contracture shortening was observed on exposure to complete metabolic blockade (2 mM cyanide in the presence of 10 mM 2-deoxyglucose). Strikingly similar contractures were observed in cells permeabilised with saponin on removal of ATP from the bathing medium. In each case, the response consisted of rapid shortening (over - 20 seconds at a peak speed of about 1.6 ~m/lOOmm-set) to - 60 % of control length. On removal of metabolic blockade, or readmission of ATP, the cell contracted further and subsequently relaxed. In permeabilised cells, the rate, and extent of shortening were Ca* independent (150 nM < [Ca++] < 10 nM, buffered with 10 mM EGTA). Using tension measurements from skinned cells exposed to low [ATP] (A. Fabiato C F. Fabiato, J. Phvsiol. 249: 497-517, 1975), we have formulated a simple model that can account both for contracture shortening and recontracture by changes in [ATP]i without changes of Cai.
s.55
Cell
Cardiol20
(Supplement
IV) (1988)
P-%THE
EFFECT OF METABOLIC SUBSTRATES ON INTRACELLULAR pi (PHI) DURING HYPOXIA IN QUIESENT SHEEP HEART PURKINJE FIBRES. C.M. Bright and D. Ellis. Department of Physiology, University Medical School, Teviot Place, Edinburgh, EH8 9AG. When oxidative phosphorylation is blocked by hypoxia there is an intracellular acidification which is followed on reoxygenation by a further transient acidification before recovery (Ellis & Noireaud, 1987. J. Physiol.382, 125-141). Cardiac tissue can utilize different metabolic substrates so the effects of glucose, pyruvate or acetate (20mM) during hypoxia were investigated. 30 minutes exposure to the substrate was followed by 20 minutes of hypoxia. In 6 experiments there appeared to be no significant difference (P>O.l in a 2 sample ttest) between hypoxia induced acidification in 20mM glucose, acetate or pyruvate compared to that in normal Tyrode (10mM glucose). This lack of significance could have been due to the wide variation in the effects of the various substrates. It is possible that the large glycogen stores of Purkinje fibres prevent the different effects of the substrates from being apparent in these relatively short term exposures. (Supported by the British Heart Foundation).
P-56
METABOLISM AND ACTION POTENTIAL SHORTENING $lJRING METABOLIC BLOCKADE AND ISCHAEMIA IN ISOLATED FERREI HEARTS. A.C. Elliott+ G.L. Smith+, D.G. Alleg+. 'Dept. of Physiology, University College London, LoAdon WClE 6BT, U.K. and Department of Physiological Sciences, University of Manchester, Manchester Ml3 9PT, U.K. Shortening of the action potential during ischaemia and metabolic blockade (inhibition of both aerobic and anaerobic metabolism) may contribute to the contractile failure which occurs under such conditions. It has been hypothesised that a decline in ATP causes the action potential shortening via the activation of ATP-sensitive Kt channels. We have measured ATP (with P-31 NMR) and action potential duration (using a suction electrode) simultaneously in isolated ferret hearts. Metabolic blockade caused a rapid fall in both contractility and action potential duration. ATP fell only slightly, and remained well above the range where activation of the ATP-sensitive I(+ channel would be expected to occur. This suggests that channel activation does not occur simply via a large fall in bulk ATP. In ischaemic hearts, we observed no fall in ATP and little action potential shortening during the development of contractile failure; taken together with other work (Eisner et al, J. Phvsiol. 390: 57P: 1987), this suggests that metabolic changes (intracellular acidosis and accumulation of inorganic phosphate) are largely responsible for contractile failure in ischaemic ferret hearts. Supported by the British Heart Foundation.
P- ,57
THE ROLE OF ATP IN ENERGY DEPRIVATION CONTRACTURE IN UNLOADED RAT VENTRICULAR MYOCYTES . C.G. Nichols & W.J. Lederer. Dept. of Physiology, Univ. Maryland School of Medicine, Baltimore, MD 21201, USA. Inhibition of high-energy phosphate production leads to the development of a contracture in ventricular muscle. Two potential mechanisms are: (1) a rise in intracellular [Ca*] (Cai); (2) a fall in intracellular [ATP] (ATPi) leading to formation of rigor bridges. In unloaded rat ventricular cells, contracture shortening was observed on exposure to complete metabolic blockade (2 mM cyanide in the presence of 10 mM 2-deoxyglucose). Strikingly similar contractures were observed in cells permeabilised with saponin on removal of ATP from the bathing medium. In each case, the response consisted of rapid shortening (over - 20 seconds at a peak speed of about 1.6 ~m/lOOmm-set) to - 60 % of control length. On removal of metabolic blockade, or readmission of ATP, the cell contracted further and subsequently relaxed. In permeabilised cells, the rate, and extent of shortening were Ca* independent (150 nM < [Ca++] < 10 nM, buffered with 10 mM EGTA). Using tension measurements from skinned cells exposed to low [ATP] (A. Fabiato C F. Fabiato, J. Phvsiol. 249: 497-517, 1975), we have formulated a simple model that can account both for contracture shortening and recontracture by changes in [ATP]i without changes of Cai.
s.55