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Cyclic AMP-mediated inhibition of cardiac sodium channel
J Mol
Fc82
Cell
Cardiol
21 (Supplement
IV) (1989)
THE STATE OF CARDIAC ADRENOCEPTORS DURING ADAPTATION TO HIGH ALTITUDE. A. Aldashev, E. Kuzmenko, V. Titov, M. Mirrakhimov. Kirghiz Institute of Cardiology, Frunze, USSR. Comparative studies of right heart beta-adrenoceptors were performed in a low altitude species (bulls) and a homologous high altitude species (yaks). Right heart chambers were taken from a slaughter-house and frozen in liquid nisrogen. After defrostjng, rough me brane fractio was isolated; the binding with [ Hl-dihydroalprena7 101 ( H-DHA) and [ HI-prazosin ( '3H-PRAZ), and adenylate cyclase activation by isoproterenol were assessed. The density of both alpha-l and beta adrenoceptors in the right heart was found to be significantly decreased in yaks as compared to bulls. Beta-adrenoceptor Bmax'in the right atrium in yaks and bulls was 13.1+1.7 and 55.4+7.4 fmol/mg, respectively, that in the right ventricle - 26.2+3.4 and 58.!?+8.2 fmol/mgT respectively. The affinity of these receptors in the former was significantly higher than in the latter. Kd values were 0.27+0.3 and 1.02+0.10 r&f in yaks and bulls, respectively. The beta-adrenoceptor activation during the right heart membrane fraction stimulation by isoproterenol was not significantly different in these two species. This suggests a much higher beta-adrenoceptor activity in yaks when calculated per mole. Thus, the cardiovascular system in high altitude animals evolved through the selection of highaffinity and highly efficient beta-receptors and, possibly, alpha-I-adrenoceptors.
FC83CYCL1C Kiyosue.
AMP-MEDIATED Department
INHIBITION OF CARDIAC of Physiology, Medical
SODIUM CHANNEL. College of Oita,
M.
Arita, Hazama,
K. Ono, T. Oita 879-56.
Japan. Isoproterenol(ISP) decreases the Imax fast of depolarized guinea-pig ventricular muscles via stimulation of B-&ceptor (Arita, M. et al, Am. J. Cardiol. 51:1433-1440, 1983), suggestinq CAMP-mediated inhibitory intervention on the Na+ channels. We studied the-effect of ISP. db-CAMP and forskolin on the Na current (INa) of enzymatically isolated ventricular myocytes from the same species with the use of patch electrode-whole cell voltage clamp methods. Ca2+ and K+ currents were blocked by the use of appropriate channel blockers under low external Na+ concentrations (60 mM) at 32-33' C. Depolarizing pulses (30 ms) of various amplitude were applied at 0.2 Hz from a holding potential of -80 mV. ISP (1 yM) significantly decreased the peak 1~~ from 6.1 to 4.0 nA (n=7) or by 34 %; the effect disappeared in the presence of atenolol (10 PM). Db-CAMP (l-5 mM) and forskolin (3 PM) mimicked ISP (1 PM) for the depressant effect on 1~~. Db-CAMP (5 mM) shifted the inactivation curve of 1~~ (h m -Em relationship) to negative direction by 3.4 mV (n=5). Results suggest that cardiac INa is suppressed by the increased levels of CAMP, presumably via altered gating mechanism as a consequence of phosphorylation of the channel protein.
FC84 CARDIAC
CELLULAR
ELECTROPHYSIOLOGICAL
EFFECTS
NORMAL
OF
PLATELET
ACTIVATING
FACTOR
DURING
PERFUSION, MYOCARDIAL ISCHAENIA AND REPERFUSION IN THE GUINEA PIG. N. A. Flores and D. J. Sheridan, Academic Cardiology Unit, St. Mary's Hospital Medical School, London W2, England. Platelet activating factor (PAF) is frequently used to study the effects of platelet activation and aggregation and is thought to have deleterious effects during myocardial ischaemia, but less is known of its electrophysiological actions in whole hear$s. WeItsed isolfied, perfused guinea pig hearts to study the effects of PAF (lo, IOand loM) during normal perfusion, global myocardial ischaemia (flow 10% of control) and reperfusion and corn ared it to PAF-free buffer (n= 5/ group). PAF reduced action potentia4 duration (APD ! during normal perfusion from 168 + 4 ms to 139 + 6 ms (PcO.02, lo- M) and from 163 + 6 ms to 140 + 5 ms (P
S.87
Fc82
Cell
Cardiol
21 (Supplement
IV) (1989)
THE STATE OF CARDIAC ADRENOCEPTORS DURING ADAPTATION TO HIGH ALTITUDE. A. Aldashev, E. Kuzmenko, V. Titov, M. Mirrakhimov. Kirghiz Institute of Cardiology, Frunze, USSR. Comparative studies of right heart beta-adrenoceptors were performed in a low altitude species (bulls) and a homologous high altitude species (yaks). Right heart chambers were taken from a slaughter-house and frozen in liquid nisrogen. After defrostjng, rough me brane fractio was isolated; the binding with [ Hl-dihydroalprena7 101 ( H-DHA) and [ HI-prazosin ( '3H-PRAZ), and adenylate cyclase activation by isoproterenol were assessed. The density of both alpha-l and beta adrenoceptors in the right heart was found to be significantly decreased in yaks as compared to bulls. Beta-adrenoceptor Bmax'in the right atrium in yaks and bulls was 13.1+1.7 and 55.4+7.4 fmol/mg, respectively, that in the right ventricle - 26.2+3.4 and 58.!?+8.2 fmol/mgT respectively. The affinity of these receptors in the former was significantly higher than in the latter. Kd values were 0.27+0.3 and 1.02+0.10 r&f in yaks and bulls, respectively. The beta-adrenoceptor activation during the right heart membrane fraction stimulation by isoproterenol was not significantly different in these two species. This suggests a much higher beta-adrenoceptor activity in yaks when calculated per mole. Thus, the cardiovascular system in high altitude animals evolved through the selection of highaffinity and highly efficient beta-receptors and, possibly, alpha-I-adrenoceptors.
FC83CYCL1C Kiyosue.
AMP-MEDIATED Department
INHIBITION OF CARDIAC of Physiology, Medical
SODIUM CHANNEL. College of Oita,
M.
Arita, Hazama,
K. Ono, T. Oita 879-56.
Japan. Isoproterenol(ISP) decreases the Imax fast of depolarized guinea-pig ventricular muscles via stimulation of B-&ceptor (Arita, M. et al, Am. J. Cardiol. 51:1433-1440, 1983), suggestinq CAMP-mediated inhibitory intervention on the Na+ channels. We studied the-effect of ISP. db-CAMP and forskolin on the Na current (INa) of enzymatically isolated ventricular myocytes from the same species with the use of patch electrode-whole cell voltage clamp methods. Ca2+ and K+ currents were blocked by the use of appropriate channel blockers under low external Na+ concentrations (60 mM) at 32-33' C. Depolarizing pulses (30 ms) of various amplitude were applied at 0.2 Hz from a holding potential of -80 mV. ISP (1 yM) significantly decreased the peak 1~~ from 6.1 to 4.0 nA (n=7) or by 34 %; the effect disappeared in the presence of atenolol (10 PM). Db-CAMP (l-5 mM) and forskolin (3 PM) mimicked ISP (1 PM) for the depressant effect on 1~~. Db-CAMP (5 mM) shifted the inactivation curve of 1~~ (h m -Em relationship) to negative direction by 3.4 mV (n=5). Results suggest that cardiac INa is suppressed by the increased levels of CAMP, presumably via altered gating mechanism as a consequence of phosphorylation of the channel protein.
FC84 CARDIAC
CELLULAR
ELECTROPHYSIOLOGICAL
EFFECTS
NORMAL
OF
PLATELET
ACTIVATING
FACTOR
DURING
PERFUSION, MYOCARDIAL ISCHAENIA AND REPERFUSION IN THE GUINEA PIG. N. A. Flores and D. J. Sheridan, Academic Cardiology Unit, St. Mary's Hospital Medical School, London W2, England. Platelet activating factor (PAF) is frequently used to study the effects of platelet activation and aggregation and is thought to have deleterious effects during myocardial ischaemia, but less is known of its electrophysiological actions in whole hear$s. WeItsed isolfied, perfused guinea pig hearts to study the effects of PAF (lo, IOand loM) during normal perfusion, global myocardial ischaemia (flow 10% of control) and reperfusion and corn ared it to PAF-free buffer (n= 5/ group). PAF reduced action potentia4 duration (APD ! during normal perfusion from 168 + 4 ms to 139 + 6 ms (PcO.02, lo- M) and from 163 + 6 ms to 140 + 5 ms (P
S.87