Evidence that oxmetidine inhibits transmembrane calcium flux in cardiac and vascular tissue

Abstract

Oxmetidine, at concentrations in excess of 1 times 10−6M, caused concentration‐dependent negative inotropic and chronotropic responses in guinea‐pig isolated heart preparations. Oxmetidine, at concentrations in excess of 1 times 10−5M, caused negative inotropic responses in guinea‐pig papillary muscle preparations. The negative inotropic responses to oxmetidine were associated with shortening of the plateau phase of the action potential. Verapamil and nifedipine caused similar shortening of the plateau phase of the action potential at equivalent negative inotropic concentrations indicating that oxmetidine may also act as a calcium antagonist. In preparations partially depolarized by raising extracellular K+ concentration, oxmetidine also exhibited negative inotropic activity and reduced the calcium‐dependent action potential. However, unlike verapamil and nifedipine, oxmetidine did not show voltage‐dependent activity. Oxmetidine, at concentrations in excess of 1 times 10−5M, inhibited Ca2+‐dependent contractions of dog saphenous vein preparations and inhibited 45Ca2+‐uptake into veins depolarized by high extracellular K+. In vivo, these calcium antagonist actions of oxmetidine were demonstrated by vasodilatation, reduction in blood pressure, bradycardia and reduced cardiac output in anaesthetized cats. Oxmetidine, at concentrations of 1 times 10−5M and above, shows properties consistent with inhibition of transmembrane Ca2+ flux. This action can be distinguished from other calcium antagonists as the effects of oxmetidine are not voltage‐dependent.

Differential Influence of Various Calcium-Modulating Compounds on Ouabain Intoxication in Isolated Rat Left Atria

“…In addition, Hi-receptor antagonists block slow action potentials induced by his tamine [40] and inhibit transmembrane cal cium influx in cardiac tissue [41], Alterna tively, protection could result from a de crease in sodium load via impairment of the Na-H exchange. The Na-H exchanger has been identified in cardiac membranes [e.g.…”

Effects of Famotidine at the Mouse Neuromuscular Junction Compared with Those of Cimetidine and Ranitidine

“…In this context, famotidine, which is reported to be 10 times as potent as ranitidine and more se lective [12], was investigated. If it is true as proposed that control of intracellular cal cium concentration is a target of some of these agents [13,14], the study and the methods presented here could be a useful tool for understanding the underlying mechanisms.…”