AJP - Cell Physiology, Vol 263, Issue 4 C780-C787, Copyright © 1992 by American Physiological Society
Carbachol induces K+, Cl-, and nonselective cation conductances in T84 cells: a perforated patch-clamp study
D. C. Devor and M. E. Duffey
Department of Physiology, School of Medicine, State University of New York, Buffalo 14214.
We used the perforated patch-clamp technique to examine cell membrane ionic
conductances in isolated cells of the human colonic secretory cell line,
T84, during exposure to the muscarinic agonist carbachol. Carbachol (100
microM) induced both outward and inward currents when the patch pipette
contained a normal intracellular-like solution, the bath contained a normal
extracellular-like solution, and the cells were intermittently voltage
clamped between K+ and Cl- equilibrium potentials. The outward current was
identified as a K+ current that averaged 483 +/- 95 pA, while the inward
current averaged 152 +/- 29 pA (n = 15). The outward and inward currents
oscillated with a synchronous frequency of 0.036 +/- 0.006 Hz; however, the
onset of the K+ current occurred an average of 457 +/- 72 ms before the
onset of the inward current. When the pipette contained a high-NaCl
solution, the bath contained a Na(+)-gluconate solution, and the cells were
intermittently voltage clamped between Cl- and Na+ equilibrium potentials,
carbachol induced both Cl- and nonselective cation currents. The Cl-
current averaged 455 +/- 73 pA, while the nonselective cation current,
averaged 336 +/- 54 pA (n = 14). No difference was observed in the onset of
these two currents. These results indicate that carbachol induces three
separate ionic conductances in T84 cells. We used the whole cell
patch-clamp technique in a previous study of these cells [D. C. Devor, S.
M. Simasko, and M. E. Duffey. Am. J. Physiol. 258 (Cell Physiol. 27):
C318-C326, 1990] and found that carbachol induced only an oscillating
membrane K+ conductance. Thus some unidentified component of the
carbachol-sensitive signal transduction pathway is diffusible and may be
lost during whole cell patch clamping.
