Effects of Calcium-Antagonistic Coronary Vasodilators on Myocardial Contractility and Membrane Potentials

Open Access
Publisher Website
Google Scholar
Abstract
To clarify the relation between negative inotropic effects of Ca-antagonistic vasodilators and their Ca-antagonistic effects, the effects of nifedipine, verapamil and diltiazem on isolated electrically-driven left atrial preparations of guinea pig were studied. Ion-specificity of antagonistic effect was studied. In normal Tyrodes solution, all 3 vasodilators produced a shift to the right of the dose-response curve for Ca, the pA2 [negative log of the concentration of antagonist that reduces the effect of a double dose of agonist to that of a single dose] values being 5.90 for nifedipine, 4.88 for verapamil and 4.07 for diltiazem. Th maximum rate of rise of action potentials recorded as a measure of the Na permeability of the membrane was apparently reduced by verapamil and diltiazem, while this rate was unaffected by nifedipine. All 3 vasodilators suppressed contractile activities induced in K-depolarized atria by isoproterenol, and the dose-response curves Ca were shifted to the right, the pA2 values being 8.24 for nifedipine, 6.67 for verapamil and 6.57 for diltiazem. In another set of experiments, Ca-dependent action potentials were evoked in the K-depolarized atria by isoproterenol or aminophylline. These action potentials were suppressed by the above 3 vasodilators at dosage levels comparable to those producing suppression of the isoproterenol-induced contractile response of the depolarized atria.

This publication has 0 references indexed in Scilit: