Carbachol induces oscillations of membrane potassium conductance in a colonic cell line, T84.
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+.
Devor
D C
DC
Department of Physiology, School of Medicine, State University of New York, Buffalo 14214.
Simasko
S M
SM
Duffey
M E
ME
D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D003110:Colonic Neoplasms; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009991:Oscillometry; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000502:physiology
D004533:Egtazic Acid; D002217:Carbachol; D002118:Calcium