Adenylate Cyclase Activity in the Superior Cervical Ganglion of the Rat

Abstract

Adenylate cyclase activity in cell-free homogenates of the rat superior cervical ganglion (SCG) was assayed under a variety of experimental conditions. Adenylate cyclase activity was decreased by approximately one-half when 1 mM EGTA was included in the homogenization buffer and assay mixture, indicating the presence of a Ca2+-sensitive adenylate cyclase in the ganglion. In the presence of EGTA, basal adenylate cyclase activity in homogenates of the SCG was 12.9 +/- 0.6 pmol cyclic AMP/ganglion/10 min. Enzyme activity was stimulated three- to fourfold by 10 mM NaF or 10 mM MnCl2. Both GTP and its nonhydrolyzable analog guanylylimidodiphosphate (GppNHp) stimulated adenylate cyclase in a concentration-dependent manner over the range of 0.1-10.0 microM. Stimulation by GppNHp was five to six times greater than that produced by GTP at all concentrations tested. Decentralization of the ganglion had no effect on basal or stimulated adenylate cyclase activity. Receptor-linked stimulation of adenylate cyclase was not obtained with any of the following: isoproterenol, epinephrine, histamine, dopamine, prostaglandin E2, or vasoactive intestinal peptide. Thus the receptor-linked regulation of adenylate cyclase activity appears to be lost in homogenates of the ganglion.