INFLUENCE OF PH CHANGES ON THE ACTIONS OF VERAPAMIL ON VASCULAR EXCITATION-CONTRACTION COUPLING

We have previously shown that pH changes alter the cardiovascular resp onses to verapamil in rat, in vivo and in isolated rat heart. The curr ent study investigated the influence of pH changes on the actions of v erapamil on potassium- or noradrenaline-stimulated contraction in rat tail arteries. The proximal 2-2.5 cm of ventral tail artery was bathed in and perfused initially (20-25 min) with physiological salt solutio n (pH 7.4) which was later made calcium-free at pH 7.4 (control), pH 7 .2 (acidosis) or pH 7.67 (alkalosis), After equilibration each artery was exposed to verapamil following which the contractile responses to increasing concentrations of calcium were recorded. The patterns of re sponses in noradrenaline- or potassium-stimulated arteries were differ ent. In normal conditions, the vasodilator effect of verapamil was pre dominant in potassium-stimulated arteries but less in the noradrenalin e-stimulated preparations. With pH changes the effect of verapamil was enhanced more in noradrenaline- than in potassium-stimulated arteries . It is postulated that pathology-induced changes in the character of calcium channels could alter the effect of calcium channel blockers.