Action of anaphylaxis and histamine on isolated mammalian ventricles: contractile hyperactivation and changes of membrane potentials.

The effects of anaphylaxis and histamine on the action potential and the isometric contraction of isolated guinea-pig papillary muscles have been investigated. The anaphylactic reaction was found to affect directly ventricular muscle fibers. The anaphylactic alterations of membrane and contraction parameters were very similar to effects of histamine and were not affected by pretreatment with reserpine. Isometric contraction developed typical features of contractile hyperactivation, characterized by a marked increase of peak force associated with shortening of time to peak of contraction and the appearance of oscillatory contractions and aftercontractions. Mechanical alternans and electrical alternans were also observed. Oscillatory contractions occurring during membrane depolarization were increased with prolongation of the action potential duration. After contractions developed after complete repolarization of the membrane and increased at higher stimulation rates. The anaphylactic reaction and histamine caused shortening of the action potential. Resting potential, overshoot and maximum rate of rise of action potential were not significantly changed. A common mechanism of contractile hyperactivation based on a multicompartment model of the intracellular Ca movements in discussed.