Cardiac electrophysiological effects of histamine, H1 and H2 agonists

Abstract

The effects of histamine, H1 and H2 agonists on the transmembrane action potentials (APs) of electrically driven left auricle of guinea-pig were studied in Tyrode and in 25 mM K+ Tyrode solution. Under physiological conditions, histamine (10−7−10−5M) increased the amplitude and the plateau phase of AP. The H1 agonist pyridylethylamine (PEA; 10−5−10−4M) exerted similar effects as histamine while the H2-agonist impromidine (10−8−10−7M) decreased the duration of AP. PEA restored the abolished electromechanical activity in high K+ (25 mM)-depolarized atria. These slow APs were unaffected by the β-adrenergic blocker pindolol (5×10−7M) but were abolished by the H1 antagonist mepyramine (10−5M). Neither dimaprit nor impromidine was able to induce slow AP. Our results suggest that in guinea-pig left atria histamine enhances the slow inward Ca2+ current mediated by H1 receptors.