α1-Adrenoceptors of rat myocardium: Comparison of agonist binding and positive inotropic response

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Abstract
Our binding experiments suggest that myocardial α1-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.