Microtubules in the "chloride cell" of the gill and disruptive effects of colchicine on the salt balance of the sea water adapted Mugil capito.

Electron-microscopic examination of the gill of the grey mullet, Mugil capito adapted to sea water, reveals the presence of numerous microtubules in the apical region of the mitochondria-rich cells. No microtubules are found in other types of epithelial cell. Exposure of the fish to colchicine (10(-4)M) for four hours induces a 20% increase of plasma Na and Cl. Colchicine leaves the water permeability of the gill unchanged but Cl and Na exchange fluxes are inhibited by 30-50% and the gill potential pattern is altered. Salt gain replaces salt excretion across the gill. The K dependent Na and Cl efflux components, independent of the gill potential shift produced by K, are totally inhibited by colchicine. Exposure to lumicolchicine is not followed by a significant change of these Na and Cl efflux-components and potential pattern. The possibility that microtubules intervene in the salt excretion process across the chloride cells is discussed.