Kinetic characterization of pigment migration and the role of the cytoskeleton in granule translocation in the red chromatophores of the shrimp Macrobrachium olfersii (Crustacea, Decapoda)

The kinetic characteristics of pigment aggregation and dispersion were exam ined in the perfused, red ovarian chromatophores of the freshwater palaemon id shrimp Macrobrachium olfersii. Aggregation, induced by either red pigmen t concentrating hormone (RPCH) or the Ca++ ionophore A23187, takes 24-26 mi n to complete. The associated velocity profiles consist of three distinct p hases: an immediate velocity peak of 13.6 +/- 3.23 and 11.6 +/- 1.15 mu m/m in, respectively, of 8-min duration; 10-min plateaus of 1.7 +/- 0.20 and 2. 2 +/- 0.29 mu m/min, respectively; and an interval in which velocity declin es irregularly and ceases. Subsequent pigment dispersion, induced by a Ca+-free saline, is likewise triphasic, attaining peak velocities of 5.0 +/- 0 .67 and 6.8 +/- 1.72 mu m/min, respectively; plateau velocities were 1.7 +/ - 0.28 and 1.4 mu m/min, respectively. The chromatophores contain two disti nct types of pigment granule, bundles of microtubules, and a well-developed smooth endoplasmic reticulum. The effects of substances that affect the dy namics of cytoskeletal components were also examined. Neither colchicine no r the dynein inhibitor vanadate affect aggregation or dispersion, although colchicine itself induces 20-60% aggregation. However, cytochalsin B partia lly inhibits aggregation and markedly affects dispersion, while butanedione monoxime (an inhibitor of myosin ATPase) also partially inhibits aggregati on and induces pigment dispersion. While the nature of the rapid component of pigment aggregation is obscure, these data suggest that the slow compone nt may result from the interaction of the pigment granules with an actin-my osin-like system. These findings are compared with the kinetic characterist ics of organelle translocation seen in fish chromatophores and neurons in w hich transport velocities are conspicuously greater than those recorded her e for shrimp chromatophores. J. Exp. Zool. 283:19-30, 1999. (C) 1999 Wiley- Liss, Inc.