Effects of arginine vasopressin and its functional analogues on contractile vacuole of Amoeba proteus: possible mechanisms of signal transduction

Study of effects of arginine vasopressin (AVP) and its functional analogues on the contractile vacuole of the amoeba Amoeba proteus has esished that AVP (10 μM) increases frequency of vacuole contractions. This effect is reproduced by antagonist of receptors of the V 2 type desmopressin (10 μM), but is suppressed by antagonist of receptors of the V 1 type. Apart from desmopressin, acceleration of the vacuole contraction is also caused by activator of adenylyl cyclase forskolin (25 μM). Cyclic adenosine monophosphate (cAMP, 1 μM) produces a dual effect on the vacuole contraction: it either increases its frequency like AVP, desmopressin, and forskolin, or suppresses the AVP effect without producing its own action. The non selective blocker of adenosine receptors aminophylline inhibits the AVP like effect of cAMP. This indicates either effect of cAMP on adenosine receptors or conversion of cAMP into adenosine through the action of 5 ectonucleotidase. In either case, we are dealing with extracellular cAMP receptors, which have been earlier established in the amoeba Dictyostelium discoideum. Results of our experiments indicate specificity of the effect of arginine vasopressin as well as a mixed character of signal transduction from membrane areas sensitive to AVP and combining features of receptors both of the V 1 and of the V2 type.