Differences in beta-adrenoceptor binding in anterior and inferior myocardial wall microsomes of normal canine left ventricle

Myocardial beta-adrenoceptor binding was investigated, with (-)3H dihydroalprenolol as radioligand, in microsomes derived from anterior (ALV) and inferior (ILV) myocardial wall sections of the canine left ventricle. Characterisation of specific binding sites revealed a hierarchy of myocardial beta-adrenoceptor binding with greater binding occurring to the anterior than the inferior wall of the left ventricle, under identical experimental conditions. Equilibrium analysis by Scatchard plots suggested a significant (P less than 0.01) difference in the number of receptors (Bmax ALV = 70 fmol . mg-1 protein vs Bmax ILV = 37 fmol . mg-1 protein) with no alteration in the binding affinity of the receptors (KDALV = 10.1 nmol . litre-1 vs KDILV = 6.7 nmol . litre-1). Such differences in the extent of binding of beta-adrenoreceptors in cardiac muscle may be of physiological and pathological significance and may account for the heterogeneity of regional autonomic responses in the heart.