Circadian rhythm of pigment migration induced by chromatrophorotropins in melanophores of the crab Chasmagnathus granulata.

The circadian rhythm of black pigment migration of melanophores of the crab Chasmagnathus granulata and the variation in responsiveness of these cells to pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide (CCAP), and red pigment-concentrating hormone (RPCH) were investigated. Melanophores of C. granulata possess an endogenous circadian rhythm of pigment migration, with black pigments staying more dispersed during the day period and more aggregated during the night period. This rhythm seems to be largely dependent on an endogenous release of neurohormones from eyestalks, and to a lesser extent on a primary response to illumination. beta-PDH was the most potent PDH isoform to induce pigment dispersion in both in vivo (EC50 = 0.4 pmol/animal) and in vitro (EC50 = 0.18 microM) assays. CCAP also induced pigment dispersion in vivo and in vitro assays (EC50 = 12 microM), but it was less potent than beta-PDH. In vivo, RPCH induced a low and nondose-dependent pigment aggregation, while in vitro, it had no effect on pigment migration. The responsiveness of melanophores of C. granulata to beta-PDH was significantly higher during the day period when compared to the night period in both assays, in vitro and in vivo. These results suggest that the endogenous circadian rhythm of black pigment migration is dependent on both endogenous circadian rhythm of beta-PDH synthesis and/or release from eyestalks and on an endogenous rhythm of responsiveness of melanophores to beta-PDH.