SENSITIVITY OF VOLUME-SENSITIVE CL- CONDUCTANCE IN HUMAN EPITHELIAL-CELLS TO EXTRACELLULAR NUCLEOTIDES

The sensitivity to extracellular nucleotides of volume-sensitive Cl- c hannel activity was investigated by whole cell and single-channel patc h-clamp recordings in a human small intestinal epithelial cell line (I ntestine 407) during steady osmotic swelling. Adenine nucleotides adde d to the bathing solution suppressed whole cell volume-sensitive Cl- c urrents with the potency sequence of ATP > ADP > AMP. In contrast, ext racellular adenosine 3',5'-cyclic monophosphate (cAMP) at over 0.1 mM increased volume-sensitive Cl- currents in the entire voltage range ex amined, whereas guanosine 3',5'-cyclic monophosphate was without effec t. Neither the single-channel conductance nor the open probability was affected by extracellular cAMP. Extracellular ATP (at over 30 mu M), in the Mg2+-free form, inhibited the whole cell volume-sensitive Cl- c urrent, preferentially in the outward direction. By exposure to extrac ellular ATP, the single Cl- channel current became flickery at positiv e potentials. These results indicate that the volume-sensitive Cl- cha nnel in the human epithelial cell is stimulated voltage independently by extracellular cAMP but blocked voltage dependently by the Mg2+-free form of extracellular ATP.