AJP - Cell Physiology, Vol 258, Issue 2 C318-C326, Copyright © 1990 by American Physiological Society
Carbachol induces oscillations of membrane potassium conductance in a colonic cell line, T84
D. C. Devor, S. M. Simasko and M. E. Duffey
Department of Physiology, School of Medicine, State University of New York, Buffalo 14214.
Effects of carbachol on membrane potential and current in T84 cells were
determined using whole cell patch-clamp techniques. When the pipettes
contained a standard KCl solution and the bath contained a standard NaCl
solution, carbachol (100 microM) caused a rapid hyperpolarization to the K+
equilibrium potential (EK+), followed by potential oscillations. When
membrane potential was clamped to 0 mV, carbachol induced an outwardly
directed K+ current in 31 of 37 cells, with a peak value of 618 +/- 51 (SE)
pA. In 77% of these cells the current oscillated and gradually declined to
base line. Atropine (20 microM) blocked this response. In symmetric KCl
solutions the carbachol-induced current reversed at 0 mV with no
rectification. Ba2+ or Cs+ did not block the current, but
tetraethylammonium ion (TEA) reduced the number of responding cells.
Although a Cl- conductance was found in resting cells, carbachol did not
cause an increase in Cl- current when the cells were voltage-clamped to
EK+, or when voltage-clamped to +/- 60 mV while bathed in symmetric NaCl
solutions. When the Ca2(+)-buffering capacity of the pipette solution was
increased, 80% of the cells responded to carbachol, but only 10%
oscillated; however, no K+ current was induced by carbachol when the
pipette was made nominally Ca2+ free. The current was not affected by
removal of Ca2+ from the bath. These results show that carbachol induces an
oscillating Ca2(+)-activated K+ conductance in T84 cells, but no Cl-
conductance. This K+ conductance is dependent on the mechanisms that
regulate intracellular Ca2+.
