α-Adrenoceptors of rat myocardium: Comparison of agonist binding and positive inotropic response.

Binding of agonists to al-adrenoceptors labelled by H-prazosin was investigated in membranes of rat myocardium and compared to the inotropic response elicited by α-adrenoceptor activation on isolated right ventricles. Our binding experiments suggest that myocardial α-adrenoceptors can exist in states of different affinity for agonists. Some agonists like adrenaline and phenylephrine seem to induce a temperature-dependent change in the conformation of the receptor which may represent a rapid form of desensitization. Since no appreciable receptor reserve was detected it is hypothesized that the high affinity state which can be measured at 0°C under equilibrium conditions may be relevant to the initiation of the functional response. [ABSTRACT FROM AUTHOR]