Chloride channels in primary cultures of seawater fish (Dicentrarchus labrax) gill

Patch-clamp experiments were undertaken on primary cultures of respiratory cells originating from sea bass (Dicentrarchus labrax) gills, A small-conductance Cl- channel of 8 pS was characterized in cell-attached configuration with 140 mM N-methyl-D-glucamine-Cl in the pipette and bath solutions. No activity was recorded below a membrane holding potential of +20 mV (-V-p, referenced to the pipette solution), and the channel showed an inward rectification. In the inside-out configuration the Cl- channel was active at all membrane holding potentials. Its open probability strongly increased with membrane depolarization. The channel activity could be increased by the application of protein kinase A + ATP. This channel was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoic acid, diphenylamino-2-carboxylic acid, and I- and was insensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The presence of Cl- channels ill the apical membrane of respiratory cells provides additional evidence for an important role of this cell type in the control of ion homeostasis of seawater fish.