Peculiarities of Signal Transduction from Arginine-Vasopressin Receptors Located on the Apical Surface of Epithelial Cells of the Frog Urinary Bladder and on the Amoeba Outer Membrane

Mechanisms of action of arginine-vasopressin (AVP) on water transport across the wall of urinary bladder of the frog R. temporaria L. and the outer membrane of the amoeba A. proteus were considered. AVP and its functional analogs were added to the basolateral and apical surfaces of the frog urinary bladder membrane and to the amoeba outer surface. In amoeba the AVP effect was evaluated from action on frequency of contractions of contractile vacuole that represents its organ of water—electrolyte homeostasis. It was shown that the system of signal transduction from the apical AVP receptors differed considerably from that located on the basolateral membrane and had a marked similarity with the system of signal transduction from AVP-sensitive structures on the outer membrane of amoeba. The urinary bladder apical membrane as well as the amoeba outer membrane has a mixed type of sensitivity to AVP with unidirectional (not antagonistic like on the basolateral membrane) involvement of systems coupled to receptors of the V₁ and V₂ type. We suggest that the system of signal transduction from apical AVP receptors corresponds to the earlier stage of evolutionary development.