Sensitivity of volume-sensitive Cl- conductance in human epithelial cells to extracellular nucleotides

The sensitivity to extracellular nucleotides of volume-sensitive Cl - channel activity was investigated by whole cell and single-channel patch-clamp recordings in a human small intestinal epithelial cell line (Intestine 407) during steady osmotic swelling. Adenine nucleotides added to the bathing solution suppressed whole cell volume-sensitive Cl- currents with the potency sequence of ATP > ADP > AMP. In contrast, extracellular adenosine 3',5'-cyclic monophosphate (cAMP) at over 0.1 mM increased volume-sensitive Cl - currents in the entire voltage range examined, whereas guanosine 3',5'-cyclic monophosphate was without effect. Neither the single-channel conductance nor the open probability was affected by extracellular cAMP. Extracellular ATP (at over 30 μM), in the Mg 2+ -free form, inhibited the whole cell volume-sensitive Cl- current, preferentially in the outward direction. By exposure to extracellular ATP, the single Cl - channel current became flickery at positive potentials. These results indicate that the volume-sensitive Cl - channel in the human epithelial cell is stimulated voltage independently by extracellular cAMP but blocked voltage dependently by the Mg 2+ -free form of extracellular ATP.