J Biol Chem, Vol. 274, Issue 46, 32762-32770, November 12, 1999

Intracellular Pathways of V₁ and V₂ Receptors Activated by Arginine Vasopressin in Rat Hippocampal Neurons

Tomohiro Omura^§, Junichi Nabekura, and Norio Akaike

From the  Department of Physiology, Graduate School of Medicine, Kyushu University, Fukuoka 812-8582 and ^§ Research Laboratories, Nippon Chemiphar Co., Ltd., Saitama 341-0005, Japan

To explore the intracellular pathways activated by vasopressin receptors, the effects of arginine vasopressin (AVP) and its analogues mediating glycine (Gly)-induced Cl currents (I_Gly) were examined in acutely dissociated rat hippocampal CA1 neurons using the whole-cell patch recording technique. AVP and its analogues inhibited I_Gly in a concentration-dependent manner. The inhibitory actions of AVP(4-9) (AVP metabolite) and NC-1900 (AVP(4-9) analogue) were reversed by a V₁ receptor antagonist, or pretreatment with 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid. In contrast, these blocking procedures had no effect on the 1-desamino-8-D-AVP (DDAVP; V₂ agonist) action. A V₂ receptor antagonist did not block the inhibitory action of AVP(4-9) or NC-1900, but blocked that of DDAVP. The inhibitory action of AVP was completely blocked by the co-application of the V₁ and V₂ antagonists. The inhibitory action of NC-1900 was not affected by perfusion with a Ca²⁺-free external solution, but was strongly blocked by thapsigargin. The intracellular application of heparin or anti-inositol 1,4,5-triphosphate (IP₃) also blocked the NC-1900 action. Furthermore, Ca²⁺/calmodulin (CaM) inhibitors blocked the NC-1900 action, while a CaM-dependent kinase II inhibitor and PKC modulators had no effect. 2',5'-Dideoxyadenosine (an adenylate cyclase inhibitor), H-89, and Rp-cAMPS blocked the inhibitory actions of NC-1900 and DDAVP. These results suggest that the activation of the V₁ receptor in the hippocampal neurons induces the production of IP₃, which releases Ca²⁺ from the IP₃-sensitive Ca²⁺ storage sites. The Ca²⁺ binds to CaM, resulting in the activation of Ca^2+/CaM-sensitive adenylate cyclases. The activation of protein kinase A through the adenylate cyclase inhibits I_Gly.