Intracellular pathways of V1 and V2 receptors activated by arginine vasopressin in rat hippocampal neurons

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 V-1 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; V-2 agonist) action. A V-1 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 V-1 and V-2 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 tan 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 V-1 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 Ca2+/CaM-sensitive adenylate cyclases, The activation of protein kinase A through the adenylate cyclase inhibits I-Gly.