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Beta-adrenoceptor subtypes in young and old rat ventricular myocytes: a combined patch-clamp and binding study

By CERBAI E., GUERRA L., VARANI K., BARBIERI M., BOREA P.A. and MUGELLI A.

Abstract

1. We used electrophysiological and binding techniques to assess the presence of beta 1- and beta 2-adrenoceptors (beta 1AR and beta 2AR) in rat cardiac myocytes and to determine their ratio during aging. Experiments were performed in left ventricular myocytes enzymatically dissociated from the heart of 3-(young) or 22-month-old (old) Wistar Kyoto rats. 2. In patch-clamp experiments, myocytes from old rats showed a prolonged action potential duration (at -20 mV: 41.7 +/- 3.6 vs 26.2 +/- 3.1 ms; at -60 mV: 154.4 +/- 17.7 vs 87.1 +/- 6.9 ms, P < 0.05) and an augmented membrane capacitance (an index of cell size) (271.7 +/- 20.2 vs 164.3 +/- 14.6 pF, P < 0.05) compared to young rats. beta 2AR stimulation, achieved by superfusing myocytes with the selective beta 2AR agonist, zinterol (10 microM) or with (-)-isoprenaline (1 microM) in the presence of the selective beta 1AR antagonist, CGP 20712A (0.1 microM), significantly increased L-type calcium current (ICa,L) in rat ventricular myocytes. The percentage increase was similar in both young and old rats, either with zinterol (26.9 +/- 3.6% and 24.2 +/- 2.8%, respectively) or isoprenaline plus CGP 20712A (30.4 +/- 3.7% and 22.4 +/- 4.1%, respectively). Isoprenaline alone (beta 1AR and beta 2AR stimulation) caused a much smaller increase in ICa,L in old rats (58.4 +/- 12.1%) than in younger ones (95.3 +/- 8.1%) (P = 0.067

Topics: adrenoceptors, rat myocytes, patch clamp, binding studies
Year: 1995
OAI identifier: oai:iris.unife.it:11392/1197911
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