IDENTIFICATION OF ALPHA-ADRENERGIC RECEPTORS IN CATFISH LIVER AND THEIR INVOLVEMENT IN GLUCOSE-RELEASE

This study aimed to characterize alpha-adrenergic receptors in catfish hepatocytes in which catecholamine-induced calcium transients have be en observed. alpha-Adrenergic binding sites were studied in purified l iver membranes using the specific alpha(1)-receptor antagonist [H-3]pr azosin. At 22 degrees C specific binding of [H-3]prazosin is saturable , reversible, and linear as a function of tissue concentration; the as sociation reaches a maximum at 15 min, and the half-time for dissociat ion is about 4 min. Analysis of binding data suggests a single class o f binding sites with a K-d of 1.6 nM and a B-max of 182.1 fmol/mg prot ein. The relative potency of selective adrenoceptor ligands points to the presence in catfish liver of a-adrenergic receptors in addition to the beta-adrenergic receptor population previously characterized. Mor eover, the binding data have been correlated to the glucose release fr om isolated hepatocytes suspended and perifused in a BioGel column, su ggesting the involvement of alpha-adrenergic receptors in the glycogen olytic response to catechiolamines in catfish hepatocytes. (C) 1994 Ac ademic Press, Inc.