The “small” conductance chloride channel in the luminal membrane of the rectal gland of the dogfish (Squalus acanthias)

Abstract

Besides the “larger” Cl⁻ channel with a single channel conductance of about 45 pS, a “small” channel was observed in the luminal membrane of the dogfish rectal gland [9]. In cell excised (inside out) patches with NaCl solution on both sides, the latter channel had a single channel conductance of 11±1 pS (n=21), and its current-voltage relationship was linear in the voltage range+90 to −90 mV. The open state probability increased moderately with negative clamp potentials. Ionic replacement studies revealed a high selectivity of Cl⁻ over gluconate, sulfate, and iodide, whereas bromide was permeable to some extent. Also the channel is impermeable for Na⁺. The Cl⁻ channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate did not affect this “small” conductance Cl⁻ channel. It can be concluded that the luminal membrane of stimulated rectal gland cells possesses two types of Cl⁻ channels, which differ markedly in their characteristics.