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Effect of insulin on sodium pump activity of mammalian myocardium
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71 THE SPECIFIC K+ EFFECT ON \i MAX ON PROPAGATEDACTION,&'& TENTIALS. L.Fu. The Cardiovascular Institute, Tokyo,Japan To study non-membrane potential dependent K+ effect on steady-state 9 max of the propagated action potential (Al?) and its recovery in premature responses, guinea pig papillary muscles (1 mm long) were mounted in 3 separate Ry increasing external K+ chamber with a Vaseline gap. (Ko) from 5.4 to 10.4, 15.4, 20.4 mti/L, mean value of RMP was changed from -84.3 (n=14) to 71.9 (n=88), -53.5 (n=4) mV, and V max was decreased from 203.0 to 168.6, 78.8, When RMP in each Ko was held at -85 mV by 5.0 V/set. passing polarizing current across gap. 3 max was restored almost completely at Ko=10.4 mn!/L (201.4 V/set), nut partly at Ko=15.4 and 20.4 mM/L (128.0 and 66.3 V/set). At KoZ25.4 mM/L inactivated 0 max was entirely unrestored even at RMP -140.0 mV. In four experiments the time constants with which 0 max in premature APs regained the steady-state value were significantly prolonged in the condition of Ko=10.4 mM/L and %IPp=-95 mV thqn that of L;o= 5.4 mM/L and the same RhTP(35.4i4.8 VS 19.5t2.3 msec, p< 0.05). Thus, K+ might affect 0 max of Al% by 00th K+induced polarization and the specific effect.
72 EFFECT OF INSULIN ON SODIUM PUMP ACTIVITY OF MAMMALIAN MYOCARDIUM. I. Imanaga. Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan Insulin stimulated sarcolemmal Na+-K+ATPase activity extracted from the dog ventricular . muscle cell, especially at lower Naf and K+ in the reaction medium. At this condition, insulin reversed the enzyme activity reduced by ouabain. Insulin increased cellular c-AMP level in the rythmically contracted ventricular papillary muscle. c-AMP reduced the enzyme activity with dose-dependency. Positive inotropic effect of insulin on the isolated ventricular papillary muscle was augmented at lower [K+],, lower low concentration of ouabain or preincuENa+],, bation of dibutyryl c-AMP. These results suggest that insulin stimulates Na-pump activity of the myocardial cell, and this is possibly one of mechanisms of positive inotropic action of this polypeptide.
71 THE SPECIFIC K+ EFFECT ON \i MAX ON PROPAGATEDACTION,&'& TENTIALS. L.Fu. The Cardiovascular Institute, Tokyo,Japan To study non-membrane potential dependent K+ effect on steady-state 9 max of the propagated action potential (Al?) and its recovery in premature responses, guinea pig papillary muscles (1 mm long) were mounted in 3 separate Ry increasing external K+ chamber with a Vaseline gap. (Ko) from 5.4 to 10.4, 15.4, 20.4 mti/L, mean value of RMP was changed from -84.3 (n=14) to 71.9 (n=88), -53.5 (n=4) mV, and V max was decreased from 203.0 to 168.6, 78.8, When RMP in each Ko was held at -85 mV by 5.0 V/set. passing polarizing current across gap. 3 max was restored almost completely at Ko=10.4 mn!/L (201.4 V/set), nut partly at Ko=15.4 and 20.4 mM/L (128.0 and 66.3 V/set). At KoZ25.4 mM/L inactivated 0 max was entirely unrestored even at RMP -140.0 mV. In four experiments the time constants with which 0 max in premature APs regained the steady-state value were significantly prolonged in the condition of Ko=10.4 mM/L and %IPp=-95 mV thqn that of L;o= 5.4 mM/L and the same RhTP(35.4i4.8 VS 19.5t2.3 msec, p< 0.05). Thus, K+ might affect 0 max of Al% by 00th K+induced polarization and the specific effect.
72 EFFECT OF INSULIN ON SODIUM PUMP ACTIVITY OF MAMMALIAN MYOCARDIUM. I. Imanaga. Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan Insulin stimulated sarcolemmal Na+-K+ATPase activity extracted from the dog ventricular . muscle cell, especially at lower Naf and K+ in the reaction medium. At this condition, insulin reversed the enzyme activity reduced by ouabain. Insulin increased cellular c-AMP level in the rythmically contracted ventricular papillary muscle. c-AMP reduced the enzyme activity with dose-dependency. Positive inotropic effect of insulin on the isolated ventricular papillary muscle was augmented at lower [K+],, lower low concentration of ouabain or preincuENa+],, bation of dibutyryl c-AMP. These results suggest that insulin stimulates Na-pump activity of the myocardial cell, and this is possibly one of mechanisms of positive inotropic action of this polypeptide.