ABSTRACT
The chlorpromazine, a calmodulin inhibitor, has been studied for its action on the contraction force and calcium current of the frog atrium fibres. Chlorpromazine (10(-5) mol/l) was observed to induce maximal increase of the contraction force that 30 min after the agent action amounted to (47.3 + 9.3)% of control. The high concentration of chlorpromazine (10(-4) mol/l) produced irreversible decrease in the contraction force. Chlorpromazine (10(-5) mol/l) increased the calcium current by (27.5 +/- 4.8)%. It is supposed that chlorpromazine increases contraction force and calcium current through the inhibition of calmodulin-dependent phosphodiesterase activity.
Subject(s)
Chlorpromazine/pharmacology , Myocardial Contraction/drug effects , Animals , Atrial Function , Heart Atria/drug effects , In Vitro Techniques , Rana ridibunda , Stimulation, ChemicalSubject(s)
Calcium Channel Blockers/pharmacology , Calcium/pharmacology , Epinephrine/pharmacology , Gallopamil/pharmacology , Myocardial Contraction/drug effects , Animals , Atrial Function , Drug Interactions , Heart Atria/drug effects , In Vitro Techniques , Rana ridibunda , Stimulation, ChemicalABSTRACT
Calcium ionophore A23187 (10(-5) M) increases the force of contraction of the frog atrium up to 27 + 4.8%. The calcium antagonists d-600 (5 X 10- M), Zn2+ (2 X 10(-5) M), Mn2+ (2 X 10(-4) M) decrease the force of contraction 50, 10 and 20%, respectively, and inhibit the positive inotropic effect of ionophore A23187. Inhibition of the ionophore effect by the blockers is determined by the ability of D-600, Zn2+ and Mn2+ to form complexes with the ionophore. Besides, the affinity of these blockers to the ionophore is higher than that of Ca2+. It is assumed that Zn2+, Mn2+ and D-600 possess higher affinity to ionophore A23187 as compared with myocardial Ca-channels. Fenigidin interacts with Ca-channels to a larger degree than with ionophore A23187.
Subject(s)
Calcimycin/pharmacology , Calcium Channel Blockers/pharmacology , Myocardial Contraction/drug effects , Animals , Dose-Response Relationship, Drug , Drug Interactions , Gallopamil/pharmacology , In Vitro Techniques , Manganese/pharmacology , Nifedipine/pharmacology , Rana ridibunda , Stimulation, Chemical , Zinc/pharmacologyABSTRACT
A dependence of the inward current across the cell membrane giant neurones at garden snail was investigated under voltage champ. It has been concluded that there are two components of the inward current: a calcium-dependent and I0. The latter current probably was carried by sodium ions. The inward Ca current (ICa) is then given as a function [Ca]2+ by: formula (see text) : KCa is a dissociation constant of the sites in outer part channel independent of membrane voltage. The experimental data are interpreted by two barrier membrane model bases of absolute reaction rate Eyring's theory.
