CL- CURRENTS OF UNSTIMULATED T84 INTESTINAL EPITHELIAL-CELLS STUDIED BY INTRACELLULAR-RECORDING

The ionic currents spontaneously present in T84 intestinal epithelial cells, a line of colonic carcinoma origin, have been studied using the whole-cell recording mode of the patch-clamp technique and the single -electrode voltage-clamp method. Patch-clamp experiments showed that n onstimulated T84 cells already possess large currents but that these t end to disappear during the course of the experiments, presumably thro ugh the dialysis of some essential cytoplasmic component against the m icropipette solution. The main charge carrier in these experiments app ears to be Cl- as judged from ion replacement. Microelectrode impaleme nt of T84 cells gave a membrane potential of around -30 mV, similar to the equilibrium potential for Cl- estimated from previously published values for intracellular Cl- concentration. Voltage-clamp experiments with a single microelectrode revealed three kinetically distinguishab le current patterns; currents decaying during hyperpolarizing voltage pulses, currents slowly activating during hyperpolarizing pulses and t ime-independent currents. The appearance of these distinct kinetic pat terns was not predictable from cell to cell, and was not dependent on extracellular Ca2+. Ionic replacement experiments suggest that the cha rge carrier was always Cl-, regardless of the kinetic pattern observed . No K+ currents appear to be present in the nonstimulated T84 cells. Exposure of T84 cells to the muscarinic agonist carbachol induced a sh ift in the membrane potential towards more negative values, consistent with an activation of a K+ conductance. Thus, we suggest that the res ting membrane potential in T84 cells is determined by the distribution of Cl-, This might imply that activation of K+ conductance could by i tself support secretion by T84 monolayers through tonically active Cl- channels.