RT Journal Article SR Electronic T1 Activation of G Proteins by Neuropeptide Y and γ-Aminobutyric AcidB Receptor Agonists in Rat Cerebral Cortical Membranes through Distinct Modes of Action JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 1250 OP 1256 VO 291 IS 3 A1 Yuji Odagaki A1 Nobuyuki Nishi A1 Shin Nakagawa A1 Tsukasa Koyama YR 1999 UL http://jpet.aspetjournals.org/content/291/3/1250.abstract AB The neuropeptide Y (NPY)-elicited increase in high-affinity GTPase activity in the rat cerebral cortical membranes was assayed and compared with the γ-aminobutyric acid (GABA)Breceptor-mediated response, representative of the conventional receptor-dependent mode of G protein activation. GABA and a selective GABAB receptor agonist, (±)-baclofen, stimulated the high-affinity GTPase activity in a concentration-dependent and saturable manner, with a strict Mg2+ dependence. On the other hand, NPY (10 μM)-stimulated high-affinity GTPase activity was detectable even in the absence of Mg2+. The concentration-response curve for NPY-induced increase in high-affinity GTPase activity in the presence of 2 mM MgCl2 revealed a biphasic pattern, and NPY (100 nM)-stimulated activity was dependent on MgCl2. In the presence of 2 mM MgCl2, the increase in high-affinity GTPase activity by 100 nM NPY was almost fully inhibited by a selective NPY Y-1 receptor antagonist, (R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]argininamide (BIBP3226), whereas the effect of 10 μM NPY was only partially antagonized by this compound. The increase in the activity by 10 μM NPY in the absence of MgCl2 was not at all inhibited by BIBP3226. The high-affinity GTPase activity was augmented by [Leu31,Pro34]NPY (porcine) but not by desamido-NPY, NPY(13-36) (porcine), or rat pancreatic polypeptide at submicromolar concentrations. These results indicate that NPY activates G proteins through two distinct modes of action: the conventional receptor-mediated pathway through NPY Y-1 receptor subtype dominant in the presence of the lower concentrations of NPY and receptor-independent, direct G protein activation driven by the higher concentrations of NPY. The American Society for Pharmacology and Experimental Therapeutics