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 .apprx. 1/2 when 1 mM EGTA [ethylene glycol bis(.beta.-aminoethyl ether) N,N,N'',N''-tetraacetic acid] 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 cAMP/ganglion per 10 min. Enzyme activity was stimulated 3- to 4-fold by 10 mM NaF or 10 mM MnCl2. Both GTP and is nonhydrolyzable analog guanylylimidodiphosphate (GppNHp) stimulated adenylate cyclase in a concentration-dependent manner over the range of 0.1-10.0 .mu.M. Stimulation by GppNHp was 5 to 6 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. The receptor-linked regulation of adenylate cyclase activity appears to be lost in homogenates of the ganglion.