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

The kinetic characteristics of pigment aggregation and dispersion were examined in the perfused, red ovarian chromatophores of the freshwater palaemonid shrimp Macrobrachium olfersii. Aggregation, induced by either red pigment concentrating hormone (RPCH) or the Ca++ ionophore A23187, takes 24–26 min to complete. The associated velocity profiles consist of three distinct phases: an immediate velocity peak of 13.6 ± 3.23 and 11.6 ± 1.15 μm/min, respectively, of 8-min duration; 10-min plateaus of 1.7 ± 0.20 and 2.2 ± 0.29 μm/min, respectively; and an interval in which velocity declines 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 μm/min, respectively; plateau velocities were 1.7 ± 0.28 and 1.4 μm/min, respectively. The chromatophores contain two distinct types of pigment granule, bundles of microtubules, and a well-developed smooth endoplasmic reticulum. The effects of substances that affect the dynamics of cytoskeletal components were also examined. Neither colchicine nor the dynein inhibitor vanadate affect aggregation or dispersion, although colchicine itself induces 20–60% aggregation. However, cytochalsin B partially inhibits aggregation and markedly affects dispersion, while butanedione monoxime (an inhibitor of myosin ATPase) also partially inhibits aggregation and induces pigment dispersion. While the nature of the rapid component of pigment aggregation is obscure, these data suggest that the slow component may result from the interaction of the pigment granules with an actin–myosin-like system. These findings are compared with the kinetic characteristics of organelle translocation seen in fish chromatophores and neurons in which transport velocities are conspicuously greater than those recorded here for shrimp chromatophores. J. Exp. Zool. 283:19–30, 1999.