D 2 dopamine receptor-induced sensitization of adenylyl cyclase type 1 is Gα s independent

Abstract

Acute activation of D 2 dopamine receptors inhibits adenylyl cyclase (EC 4.6.1.1), whereas persistent activation of these inhibitory receptors results in a compensatory increase in cyclic AMP accumulation. This sensitization of adenylyl cyclase is thought to involve enhanced Gα s-adenylyl cyclase interactions; however, the absolute requirement of Gα s has not been determined. The present study used a Gα s-deficient cell line to examine directly the role of Gα s in D 2 dopamine receptor-induced sensitization of recombinant adenylyl cyclase type 1 (AC1) and 5 (AC5). In acute experiments, quinpirole activation of the D 2 dopamine receptor inhibited AC1 and AC5 activity, indicating that the acute regulatory properties of AC1 and AC5 were retained in the absence of Gα s. Subsequent experiments revealed that short-term (2 h) activation of the D 2 dopamine receptor resulted in significantly enhanced forskolin-stimulated AC1 activity in the absence of Gα s, whereas sensitization of forskolin-stimulated AC5 activity appeared to require Gα s. The Gα s-independent sensitization of AC1 was explored further using AC1-selective activation protocols (A23187 and CCE) following short- and long-term agonist treatment. These studies revealed that persistent activation of D 2 dopamine receptors sensitized AC1 activity to Ca 2+ stimulation in cells devoid of endogenous Gα s and demonstrate directly that sensitization of AC1 is Gα s-independent.