Calcium‐dependent Desensitization of Adenylate Cyclase in Rat Cerebral Cortical Slices

Abstract

Incubation of slices of rat cerebral cortical gray matter in Krebs-Ringer bicarbonate-glucose buffer induced a rapid decline in the responsiveness of the adenylate cyclase in subsequently prepared membrane preparations to stimulation by various activators of the enzyme. The loss of responsiveness was time- and temperature-dependent, showed an absolute dependence on extracellular Ca ions, and was mimicked by the presence of serine proteases in the incubation medium. The resultant adenylate cyclase preparation was partially responsive to activation by fluoride and guanylylimidodiphosphate but had become virtually unresponsive to activation by ganglioside, trypsin, or .beta.-adrenergic agonists. The loss of responsiveness of adenylate cyclase was not altered if slices were incubated with depolarizing agents, putative neurotransmitters, receptor blockers, serine protease inhibitors, or adenosine deaminase. The nature of the Ca-dependent mechanism involved in the loss responsiveness of membranal adenylate cyclase is unknown. A suggested mechanism for the loss of sensitivity is the action of a membrane-bound, Ca-dependent protease.