VASOPRESSIN V-1-RECEPTOR STIMULATION PRODUCES A POSITIVE INOTROPIC RESPONSE WITHOUT AFFECTING PH(I) IN GUINEA-PIG PAPILLARY-MUSCLES

Effects of arginine-vasopressin (AVP) on the contractile force, action potential (AP) and intracellular pH (pH(i)) were studied in isolated guinea pig papillary muscles using conventional and ion-selective microelectrode techniques. AVP increased the developed tension and the resting tension, and these responses were attenuated by the V-1-receptor antagonist OPC-21268 (1-(1-[4-(3-acetylaminopropoxy)benzoyl]-4-piperidyl)-3,4-dihydro-2(1H)-quiolinone). However, AVP failed to affect AP configuration or pH(i). These results suggest that AVP produces a positive inotropy by mechanism(s) other than intracellular alkalinization.