Abstract
Epithelial cells from the intrahepatic bile duct contribute to bile formation, but little is known of the cellular mechanisms responsible. In these studies, we have characterized the endogenous GTP-binding proteins (G proteins) present in these cells and evaluated their role in regulation of high conductance anion channels. G proteins were identified in purified plasma membranes of isolated bile duct epithelial cells using specific antisera on Western blots, and ion channel activity was measured in excised inside-out membrane patches using patch-clamp recording techniques. In patches without spontaneous channel activity, addition of cholera toxin to the cytoplasmic surface had no effect (n=10). Addition of pertussis toxin caused an activation of channels in 13/34 (38%) attempts, as detected by an increase in channel open probability. Activated channels were anion selective (gluconate/Cl- permeability ratio of 0.17±0.04) and had a unitary conductance of ∼380 pS. Channel open probability was also increased by the nonhydrolyzable GDP analogue guanosine 5′-0-(2-thiodiphosphate) in 8/14 (57%) attempts. In contrast, channel open probability was rapidly and reversibly decreased by the nonhydrolyzable analogue of GTP 5′guanylylimidodiphosphate in 7/9 (78%) attempts. Western blotting with specific antisera revealed that both Giα-2 and Giα-3 were present in significant amounts, whereas Giα-1 and Goα were not detected. These studies indicate that in bile duct epithelial cells, high conductance anion channels are inhibited, in a membrane-delimited manner, by PTX-sensitive G proteins.
Original language | English (US) |
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Pages (from-to) | 253-261 |
Number of pages | 9 |
Journal | The Journal of Membrane Biology |
Volume | 133 |
Issue number | 3 |
DOIs | |
State | Published - May 1993 |
Keywords
- bile secretion
- epithelial transport
- patch clamp
ASJC Scopus subject areas
- Biophysics
- Physiology
- Cell Biology