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 m M 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 m M)-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.
ASJC Scopus subject areas
- Pharmacology (medical)