α 1‐Adrenoceptors in the conduction system of rat hearts

Abstract

We have characterized α1‐adrenoceptor in the conduction systems of the rat heart by quantitative autoradiography. Consecutive 20 μm thick sections from a single rat heart containing the sinoatrial (SA) node and atrioventricular (AV) node were incubated with increasing concentrations of [3H]‐prazosin with or without 10 μm phentolamine. After exposure to 3H‐Ultrofilm, optical densities corresponding to the SA node and AV node were determined by computerized densitometry after comparison with 3H standards. The SA node and AV node were stained heavily for cholinesterase and they contained a higher concentration of α1‐adrenoceptors than the adjacent myocardium without a significant change in the affinity. These results support the hypothesis that α1‐adrenoceptors may play an important role not only in inotropism but also in chronotropism of rat hearts. 1994 British Pharmacological Society