| Abstract: | The patch-clamp technique was used to study the effects ofcarbachol (CCh) on HT-29 cells. During CCh exposure, the cells (n = 23) depolarized close to theequilibrium potential forCl ( ; 48 mV) and the membrane potential then started to oscillate(16/23 cells). In voltage-clamp experiments, similar oscillations inwhole cell currents could be demonstrated. The whole cell conductanceincreased from 225 ± 25 pS in control solution to 6,728 ± 1,165 pS (means ± SE, n = 17). Insubstitution experiments (22 mMCl in bath solution, = 0 mV), the reversal potential changed from 41.6 ± 2.2 mV(means ± SE, n = 9) to 3.2 ± 2.0 mV (means ± SE, n = 7).When the cells were loaded with the calcium-sensitive fluorescent dye,fluo 3, and simultaneously patch clamped, CCh caused a synchronousoscillating pattern of fluorescence and membrane potential. Incell-attached patches, the CCh-activated currents reversed at arelative membrane potential of 1.9 ± 3.7 mV (means ± SE,n = 11) with control solution in thepipette and at 46.2 ± 5.3 mV (means ± SE,n = 10) with a 15 mMCl solution in the pipette.High K+ (144 mM) did not changethe reversal potential significantly (P  0.05, n = 8). In inside-out patches,calcium-dependent Clchannels could be demonstrated with a conductance of 19 pS(n = 7). It is concluded that CChcauses oscillations in membrane potential that involvecalcium-dependent Clchannels and a K+ permeability. |
