Subcellular fractions of cyclic AMP and cyclic AMP-dependent protein kinase and the positive inotropic effects of selective beta 1- and beta 2-adrenoceptor agonists in guinea pig hearts

Journal of Cardiovascular Pharmacology
H YabanaT Nagao

Abstract

We studied the effects of a full beta 1-adrenoceptor agonist (T-0509), a beta 2-adrenoceptor agonist (procaterol) and a nonselective beta-adrenoceptor agonist (isoproterenol, ISO) on subcellular cyclic AMP levels and cyclic AMP-dependent protein kinase (cyclic AMP-PK) activity in guinea pig hearts and compared them with the effect of each drug on cardiac contractility. T-0509 (10(-8)M) and ISO (3 x 10(-8)M) caused an increase of approximately 170% in dF/dtmax, whereas 10(-7) procaterol produced only a 25% increase. All these agonists significantly increased the cyclic AMP level in ventricular homogenate. Subcellular fractions were obtained by centrifugation at 100,000 g for 10 min and by Li2SO4 precipitation of the 100,000-g supernatant. In the control heart, probably salcolemmal protein, phospholamban, and 60-kDa protein in the particulate fraction and probably troponin I and troponin C in the supernatant fraction were mainly phosphorylated by the catalytic subunit of cyclic AMP-PK. In the precipitate obtained from the supernatant fraction with Li2SO4, probably all proteins described were contained. However, none of the proteins were detected in the supernatant obtained with Li2SO4. T-0509 and ISO caused significant changes in...Continue Reading

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