The mechanism of microtubule-dependent movement of pigment granules in teleost chromatophores.

The relationship of cytoplasmic microtubules to intracellular transport has been investigated in teleost chromatophores. Antimitotic agents, including colchicine, vinblastine, hydrostatic pressure, and low temperature remove microtubules in these cells and simultaneously disrupt the alignment and arrest the movement of pigment granules. During recovery, the return of alignment and movement corresponds in both time and space with the repolymerization of microtubules. These results demonstrate that microtubules are essential for the intracellular transport of pigment. Investigations of the mechanism of movement show that microtubules do not change in number or location during the redistribution of pigment in Fundulus melanophores. Microtubules in melanophores also behave as semi-stable organelles as determined by investigation with colchicine and hydrostatic pressure. These observations and others rule out a push-pull mechanism based on the polymerization and depolymerization of microtubules or one that distinguishes two operationally different sets of microtubules. It is proposed instead that particles move by sliding along a fixed array of microtubules.