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

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Abstract
Myocardial β-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 β-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 < 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 β-adrenoreceptors in cardiac muscle may be of physiological and pathological significance and may account for the heterogeneity of regional autonomic responses in the heart.