Histamine and abnormal automaticity in barium- and strophanthidin-treated sheep Purkinje fibers

Abstract

We used intracellular microelectrodes to study the effects of histamine on both normal and abnormal automaticity in sheep Purkinje fibers. Histamine, dimaprit and 4-methylhistamine caused a similar reduction of the action potential duration in driven Purkinje fibers. Histamine (10-6 M) induced spontaneous activity in p previously quiescent preparations more often than did equimolar concentrations of dimaprit and 4-methylhistamine. The effects of histamine on automaticity were enhanced in the presence of barium In fact histamine, at concentrations which were unable to induce automaticity in normal preparations, induced it in the presence of barium. In Purkinje fibers manifesting barium-induced automatic activity, histamine (10-7--10-6M) significantly increased the average number of spontaneous action potentials and shortened the time of their appearance. In the same range of concentrations, histamine dose-dependently increased the iological manifestation of calcium overload. Histamine (10-6--10-4M) increased the OAP amplitude of strophanthidin -treated Purkinje fibers, eventually inducing triggered extrabeats. All these previously described effects were selectively blocked by cimetidine (10-5 M). It is concluded that histamine may induce cardiac arrhythmias under conditions of calcium overload and that this effect may be due to induction or enhancement of oscillatory afterpotentials.

The Roles of Cardiovascular H2-Histamine Receptors Under Normal and Pathophysiological Conditions

“…These slow potentials were elicited by histamine (1–10 µM) in K + (20–30 mM) depolarised papillary muscles (e.g., Barbieri et al, 1991 ). They, however, indicated a possible direct or indirect effect of histamine on the cardiac L-type Ca 2+ channel current (I Ca.L ), which is in line with the finding that histamine can elicit spontaneous APls in Purkinje fibres in sheep ( Cerbai et al, 1990 ). Accordingly, in guinea pig atrial myocytes, histamine enhanced the intracellular Ca 2+ -concentration measured by Indo-1 (a calcium indicator) fluorescence via H 1 -histamine receptors in a nifedipine-sensible way ( Yoshimoto et al, 1998 ).…”

“…They injected histamine (bolus 0.1–10 mg) and/or diphenhydramine (bolus 3 mg, as an H 1 -histamine-receptor antagonist) in the venous inflow tubing near the entrance of the right heart ( Flacke et al , 1967 ). Cerbai et al (1990) used isolated Purkinje fibers from sheep heart obtained from a slaughterhouse (age and sex not reported). These isolated Purkinje fibers were electrically stimulated and transmembrane action potentials were recorded ( Cerbai et al , 1990 ).…”

“… Cerbai et al (1990) used isolated Purkinje fibers from sheep heart obtained from a slaughterhouse (age and sex not reported). These isolated Purkinje fibers were electrically stimulated and transmembrane action potentials were recorded ( Cerbai et al , 1990 ). They used 1–100 µM of 4-methylhistamine or dimaprit as H 2 -histamine receptor agonists and 10 µM cimetidine as H 2 -histamine receptor antagonist ( Cerbai et al , 1990 ).…”

“…These isolated Purkinje fibers were electrically stimulated and transmembrane action potentials were recorded ( Cerbai et al , 1990 ). They used 1–100 µM of 4-methylhistamine or dimaprit as H 2 -histamine receptor agonists and 10 µM cimetidine as H 2 -histamine receptor antagonist ( Cerbai et al , 1990 ). Likewise, Purkinje fibers were isolated from sheep hearts obtained from a slaughterhouse (age and sex not reported) electrically stimulated in the presence of low potassium ion concentrations (0.53 mM, Mugelli et al , 1980 ).…”