D2 dopamine receptor-induced sensitization of adenylyl cyclase type 1 is Gαs independent

Acute activation of D2 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 Gαs-adenylyl cyclase interactions; however, the absolute requirement of Gαs has not been determined. The present study used a Gαs-deficient cell line to examine directly the role of Gαs in D2 dopamine receptor-induced sensitization of recombinant adenylyl cyclase type 1 (AC1) and 5 (AC5). In acute experiments, quinpirole activation of the D2 dopamine receptor inhibited AC1 and AC5 activity, indicating that the acute regulatory properties of AC1 and AC5 were retained in the absence of Gαs. Subsequent experiments revealed that short-term (2 h) activation of the D2 dopamine receptor resulted in significantly enhanced forskolin-stimulated AC1 activity in the absence of Gαs, whereas sensitization of forskolin-stimulated AC5 activity appeared to require Gαs. The Gαs-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 D2 dopamine receptors sensitized AC1 activity to Ca2+ stimulation in cells devoid of endogenous Gαs and demonstrate directly that sensitization of AC1 is Gαs-independent.