CELLULAR SIGNALING OF PCH-INDUCED PIGMENT AGGREGATION IN THE CRUSTACEAN MACROBRACHIUM-POTIUNA ERYTHROPHORES

The cellular system responsible for the transduction of the pigment-co ncentrating hormone (PCH) signal was investigated in erythrophores of the freshwater shrimp, Macrobrachium potiuna. Dose-response curves to the hormone were determined in the absence and in the presence of seve ral drugs that affect sequential steps of the Ca2+-dependent signallin g pathway. Additionally, the ability of forskolin to induce pigment di spersion was evaluated. Neomycin sulphate (10(-4) and 10(-3) mol.l(-1) ), trifluoperazine (10(-5) and 10(-4) mol.l(-1)), 1-(5-isoquinolinesul fonyl)-2-methylpiperaz (10(-7) and 10(-5) mol.l(-1)) and okadaic acid (10(-7) mol.l(-1)) significantly (P < 0.05) decreased the responses to PCH. However, okadaic acid at low concentration (10(-9) mol.l(-1)) an d cyclosporin A (10(-6) and 10(-5) mol.l(-1)) did not significantly (P > 0.05) affect PCH activity, Forskolin (10(-4) mol.l(-1)) was able to half-maximally reverse the hormone-induced aggregation. Our results s uggest that the pigment-concentrating hormone induces pigment aggregat ion through a Ca2+-dependent pathway with a posteriori phosphatase act ivation, probably the serine/threonine phosphatase 1.