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Affinity of isoproterenol for the beta-adrenergic receptor regulating the “Slow inward current” during slow rising phase or early plateau of ventricular muscle fiber of dogs
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AFFINITY OF ISOPROTERENOL FOR THE BETA-ADRENERGIC RECEPTORREGULATINGTHE "SLOW INWARDCURRENT"DURING SLOWRISING PHASEOR EARLY PLATEAUOF VENTRICULAR MUSCLEFIBER OF DOGS. S.HIRAKAWA, K.HIEI, N.SUGISHITA AND T.SHIBAZAKI. Dept. of Medicine, Gifu University Using micro-electrode technique, the action potential(AP) of dog's ventricular muscle fiber were recorded. Details of the slow rising phase(SRP) of Al? or plateau (at the end of 5 and 10 msec after the start of the AP, termed PPs and PP,o, respectively) were recorded. Isoproterenol augmented the depolarization of PPs and PPlo. Effects of IS0 on PPg and PPlowere measured at the same level of spike potential. We plotted the inverse of effect, i.e., l/APPg and l/APPloagainst the inverse of IS0 concentration. From such Lineweaver-Burk's plot, we obtained the value of K, i.e., the dissociation constant of the drug-receptor complex. The value of K was 3.3x10~g.~-1(1.5x16~*L-1).
Practolol
effect
of IS0 in the manner of competitive
On the
other
hand,
manganese
inhibited
ion(l-2.5mM)
effect of IS0 in a manner of noncompetitive (unchanged K).
the
inhibition. inhibited
the
inhibition
FACILITATION BY BARIUM OF CALCIUM-DEPENDENT SLOWACTION POTENTI'ALSIN GUINEA PIG VENTRICULARMUSCLE. T. Ehara, Faculty of MediM. Inazawa. Department of Physiology, cine, Kyushu University, Fukuoka 812, Japan. Effects of Ba ions on the graded slow excitation and on the passive electrical properties were studied in partially depolarized guinea pig papillary muscles. On adding 0.2 mM Ba to K-rich(27 mM) Tyrode, the muscle began to show all-or-none action potentials with a disWhen [Cal, was changed (O-9+ tinct stimulus threshold. 7.2 mM) under this condition, the electrical activity varied nearly in a manner expected for a Ca-electrode. Conventional cable analysis with partition method indicated that 0.2 mM Ba caused a marked increase in the The resting membrane.resistance of depolarized muscle. results show that Ba ions in concentration as low as 0.2 mM facilitate the Ca-mediated action potentials and that this effect results at least partly from a decreased membrane shunting conductance, probably a reduction in potassium conductance.
AFFINITY OF ISOPROTERENOL FOR THE BETA-ADRENERGIC RECEPTORREGULATINGTHE "SLOW INWARDCURRENT"DURING SLOWRISING PHASEOR EARLY PLATEAUOF VENTRICULAR MUSCLEFIBER OF DOGS. S.HIRAKAWA, K.HIEI, N.SUGISHITA AND T.SHIBAZAKI. Dept. of Medicine, Gifu University Using micro-electrode technique, the action potential(AP) of dog's ventricular muscle fiber were recorded. Details of the slow rising phase(SRP) of Al? or plateau (at the end of 5 and 10 msec after the start of the AP, termed PPs and PP,o, respectively) were recorded. Isoproterenol augmented the depolarization of PPs and PPlo. Effects of IS0 on PPg and PPlowere measured at the same level of spike potential. We plotted the inverse of effect, i.e., l/APPg and l/APPloagainst the inverse of IS0 concentration. From such Lineweaver-Burk's plot, we obtained the value of K, i.e., the dissociation constant of the drug-receptor complex. The value of K was 3.3x10~g.~-1(1.5x16~*L-1).
Practolol
effect
of IS0 in the manner of competitive
On the
other
hand,
manganese
inhibited
ion(l-2.5mM)
effect of IS0 in a manner of noncompetitive (unchanged K).
the
inhibition. inhibited
the
inhibition
FACILITATION BY BARIUM OF CALCIUM-DEPENDENT SLOWACTION POTENTI'ALSIN GUINEA PIG VENTRICULARMUSCLE. T. Ehara, Faculty of MediM. Inazawa. Department of Physiology, cine, Kyushu University, Fukuoka 812, Japan. Effects of Ba ions on the graded slow excitation and on the passive electrical properties were studied in partially depolarized guinea pig papillary muscles. On adding 0.2 mM Ba to K-rich(27 mM) Tyrode, the muscle began to show all-or-none action potentials with a disWhen [Cal, was changed (O-9+ tinct stimulus threshold. 7.2 mM) under this condition, the electrical activity varied nearly in a manner expected for a Ca-electrode. Conventional cable analysis with partition method indicated that 0.2 mM Ba caused a marked increase in the The resting membrane.resistance of depolarized muscle. results show that Ba ions in concentration as low as 0.2 mM facilitate the Ca-mediated action potentials and that this effect results at least partly from a decreased membrane shunting conductance, probably a reduction in potassium conductance.