CYTOSKELETON AND PCH-INDUCED PIGMENT AGGREGATION IN MACROBRACHIUM-POTIUNA ERYTHROPHORES

Herein we report the effects of microtubule- and actin-like filament d isrupting drugs, as well as the microtubule stabilizer taxol, on PCH-i nduced pigment granule aggregation within erythrophores of the freshwa ter crustacean Macrobrachium potiuna. Dose-response curves (DRCs) to t he pigment-concentrating hormone PCH were determined under control and experimental conditions to evaluate the effects elicited by the cytos keleton-affecting drugs. Colchicine, at temperatures 22 degrees C and 4 degrees C, and vinblastine significantly inhibited the aggregating r esponse to PCH and affected the dynamics of the process, as shown by t he change in the slope of the regression curve calculated from the DRC s. Lumicolchicine, a colchicine analogue with no affinity for tubulin, also inhibited pigment migration, though no change in the slope of th e regression curve was observed. The inhibitory effects of lumicolchic ine demonstrate that changes in sites other than cytoskeleton, such as membrane permeability, may also cause a decrease in the PCH-induced a ggregating responses and that the colchicine effects may result from i ts action on cellular sites additional to the cytoskeleton. Taxol, a m icrotubule stabilizer, did not affect the DRC to PCH, and DMSO improve d the PCH evoked responses, pointing out to the maintenance of tubulin in the polymerized state as the appropriate condition for aggregation . Cytochalasin B, an actin-like filament disrupter, diminished the agg regating responses to the hormone, with no change in the slope of the regression curve, indicating that these elements take part in the proc ess and that cytosolic calcium rise, sol/gel transformations and endop lasmic reticulum motility may well play an important role in granule m igration. It is suggested that microtubules are steadily polymerized a s a requirement for pigment aggregation and that the process is biphas ic, the initial phase being dependent on the microtubule integrity.