The roles of alpha- and beta-adrenoceptors in the chronotropic responses to norepinephrine in carp heart (Cyprinus carpio) |
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| Authors: | K Temma Y Komazu Y Shiraki T Kitazawa H Kondo |
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| Institution: | Department of Veterinary Pharmacology, School of Veterinary Medicine and Animal Sciences, Kitasato University, Aomori, Japan. |
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| Abstract: | 1. The chronotropic effect of norepinephrine was studied in isolated spontaneously beating atrial preparations of carp (Cyprinus carpio) heart. 2. Norepinephrine, 0.1 microM, caused a positive chronotropic effect, while at 1 microM it caused either a positive or a negative chronotropic effect. The positive chronotropic effect, observed in 13 preparations, was potentiated by phentolamine and almost completely blocked by propranolol. 3. The negative chronotropic effect observed in the other 5 preparations was greater in the presence of propranolol, reduced by phentolamine and not affected by atropine. 4. These results indicate that alpha- and beta-adrenoceptors may coexist, mediating the negative and positive chronotropic effects, respectively, in isolated atrial preparations of carp heart. |
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