Apical Membrane Potassium Conductance in Guinea Pig Gallbladder Epithelial Cells

摘要

The fractional resistance of the apical membrane (fRa) of guinea pig gallbladder epithelial cells was observed to vary with changes in apical membrane potential (Va). Depolarizing Va from a base-line potential of -60 to -30 mV decreased fRa from 0.79 + or - 0.03 to 0.59 + or - 0.05. A comparable hyperpolarization had no effect on fRa. The potassium channel blocker tetraethylammonium (TEA) inhibited the changes in fRa induced by voltage when added to the mucosal but not when added to the serosal solution. Mucosal addition of barium (2+) and decreased pH also inhibited changes in fRa, whereas guinidine and 4-amino-pyridine did not. These results indicate that an increase in the potassium ion conductance of the apical membrane is responsible for changes in fRa with TEA-sensitive pathway was determined from differences in transepithelial current in the presence and absence of maximally effective concentrations of TEA and analyzed with respect to the Goldman constant-field equation. Computer-generated, best-fit analysis to the data indicated that they cannot be easily reconciled with potassium ion movement through a voltage independent pathway or channel. Taken together, the results suggest that activation of a voltage-dependent potassium ion conductance in the apical membrane is responsible for changes in fRa with Va. This conductance also appears to be calcium (2+)-sensitive as ionomycin caused a shift in the relation between Va and fRa. Reprints. (aw)