A maxi Cl- channel in cultured pavement cells from the gills of the freshwater rainbow trout Oncorhynchus mykiss

Primary cultures of pavement cells from the gills of a freshwater fish, the rainbow trout Oncorhynchus mykiss, have been studied for the first time us ing the patch-clamp technique. Gigaohm seals were obtained in approximately 95 % of cells studied, and channel activity was evident in a high proporti on (> 90 %), A large-conductance Cl- channel was evident in 6 % of cell-att ached and in 31 % of inside-out patches. Single-channel conductance in insi de-out patches was 372 pS, and current/voltage relationships were linear ov er the range -60 to +60mV. The channel was activated by patch excision, and activation was often associated with polarization of the patch. The mean n umber of channels per patch was 1.9, and there were several subconductance states. The relationship between channel activity (NP0) and voltage was in the form of an inverted U, and channel activity was highest between 0 and 20mV, Large-conductance Cl- channels showed a progressive time-dependent re duction in current in response to sustained polarization to voltages outsid e the range -20mV to +20mV, Permeability ratios (P) of Cl- to other anions were P-HCO3/P-Cl=0.81, P-SO4/P-Cl=0.31 and P-isethionate/P-Cl=0.53. The cha nnel was blocked by Zn2+, SITS, DIDS and diphenylamine carboxylate, This is the first description of a large-conductance Cl- channel in gill cells fro m freshwater or marine species. Possible functions of the channel are discu ssed.