Vasopressin V₁-Receptor Stimulation Produces a Positive Inotropic Response without Affecting pH_i in Guinea Pig Papillary Muscles

Abstract

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 ionselective microelectrode techniques. AVP increased the developed tension and the resting tension, and these responses were attenuated by the V₁-receptor antagonist OPC-21268 (1-{1-[4-(3-acetylaminopropoxy)benzoyl]-4-piperidyl}-3, 4-dihydro-2(1H)-quinolinone). 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.