INFLUENCE OF SALMON MELANIN-CONCENTRATING HORMONE ON VASOPRESSIN ANALOG (DDAVP) ACTIVITY AND SODIUM-TRANSPORT IN FROG-SKIN

Salmon melanin-concentrating hormone (sMCH) is a peptide known to regu late skin pigmentation both in fish and tetrapod (frog and lizard). To evaluate the influence of sMCH on ionic transport in frog skin, stand ard voltage-clamp technique for the measurement of transepithelial sho rt-circuit current (I-sc) reflecting net sodium transport was used. It was found that sMCH alone applied at concentrations of 0.5; 5 or 10 m u mol/l failed to influence I-sc. The application of 5 mu mol/l of sMC H, however, inhibited I-sc across the skin stimulated by a synthetic a nalogue of vasopressin (dDAVP), whereas no influence on natriferic eff ect of 1 mu mol/l forskolin by the studied peptide was observed. The r esults indicate that cAMP was presumably not involved in the mediation of sMCH action in frog skin. We assume that the interaction of sMCH w ith the basolateral membrane could lead either (1) to changes of membr ane structure including organization of its lipid surrounding or (2) t o modification of AVP/dDAVP receptor activity and binding capacity. Th e nature of these interactions and change(s) in cell membrane and sign al(s) which trigger processes responsible for the inhibitory effect of siMCH on dDAVP-stimulated frog skin sodium transport remains to be el ucidated.