HETEROGENEITY OF ALPHA-1-ADRENERGIC RECEPTORS IN THEIR NORADRENALINE AFFINITY IN RAT VAS-DEFERENS MEMBRANES

The affinity of alpha1-adrenoceptors of rat vas deferens membranes to noradrenaline was investigated by the radioligand method. It was shown that the binding of the specific alpha1-antagonist [H-3]WB4101 is characterized by a monophasic saturation curve. Noradrenaline competition curves with [H-3]WB4101 are biphasic, have the Hill coefficient less than 1.0 (0.6 1 +/- 0.05) exhibiting heterogeneity of alpha1-adrenoceptors in noradrenaline affinity. Nonlinear regression analysis of the data using the computer program LIGAND indicated that alpha1-adrenoceptors of rat vas deferens membranes are subdivided into two pools with high and low affinity to noradrenaline (K(d) = 0.045 +/- 0.006 muM and 1.175 +/- 0.217 muM). The results obtained are in accord with the physiological data on the presence in the rat vas deferens of two pools of functional alpha1-adrenoceptors: those with high and low sensitivity to noradrenaline.