Protistology 3 (1) 4–8 (2003) Effects of arginine-vasopressin and its functional analogues on contractile vacuole of Amoeba proteus:
possible mechanisms of signal transduction
Ya.Yu. Bagrov, N.B. Manusova and E.R. Nikitina
Laboratory of Comparative Physiology and Biochemistry of Tissue Barriers,
Sechenov Institute of Evolutionary Physiology and Biochemistry RAS, St. Petersburg, Russia
Summary
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 V2 type desmopressin (10 µM), but is suppressed by antagonist of
receptors of the V1 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 V1
and of the V2 type. Key words: water transport, arginine-vasopressin, cyclic adenosine monophosphate,
adenosine, Amoeba proteus, contractile vacuole
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