Possible role of slow sodium-calcium channels in the mechanism of changes in electrical and mechanical activity of guinea pig heart cells in local anaphylaxis (the isoptine effects).

The local anaphylactic reaction and the effects of histamine during blocking of the slow sodium-calcium channels by isoptine were investigated in the spontaneously contracting oracle of the atrium of a guinea pig previously sensitized to egg albumin. Simultaneously with the intracellular recording of the potentials, isometric contractions of the preparation were recorded by means of a mechanotron. The investigation showed that egg albumin (0.2 mg/ml) and histamine (0.1 mg/ml) are antagonists of isoptine (2-16 mg/liter) as regards its effect on automatic contraction and duration of the action potential. It is postulated that this anaphylatic reaction is based on activation of the slow sodium-calcium channels in the surface membrane of the myocardial fibers.