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G-proteins mediate intestinal chloride channel activation
B C Tilly1, M Kansen, P G van Gageldonk
1Department of Biochemistry, Medical Faculty, Erasmus University, Rotterdam, The Netherlands.
The Journal of Biological Chemistry
|February 5, 1991
Summary
G-proteins modulate intestinal epithelial cell chloride channels. Guanosine 5'-(3-thio)phosphate (GTPγS) activates a novel apical chloride channel, suggesting a new pathway for salt transport.
Area of Science:
- Cell Biology
- Ion Transport
- Gastroenterology
Background:
- GTP-binding regulatory proteins are localized in intestinal epithelial cell apical membranes.
- Their presence suggests a potential role in modulating apical chloride (Cl-) channels.
Purpose of the Study:
- To investigate the role of G-proteins in regulating apical Cl- channels in intestinal epithelial cells.
- To identify potential novel pathways for transepithelial salt transport.
Main Methods:
- Utilized membrane vesicles from rat small intestine and human HT29-cl.19A colon carcinoma cells.
- Assessed Cl- conductance using 125I- uptake and SPQ quenching.
- Performed patch clamp analysis on apical membrane patches of HT29-cl.19A colonocytes.
Main Results:
- Guanosine 5'-(3-thio)phosphate (GTPγS) significantly increased Cl- conductance, independent of K+ channels and cytosolic messengers like ATP, cAMP, and Ca2+.
- Patch clamp revealed a GTPγS-activated, inwardly rectifying, anion-selective channel with a unitary conductance of 20 ± 4 pS.
- GTPγS dramatically increased the channel's open time probability (Po) to 0.81 ± 0.09.
Conclusions:
- A novel, distinct G-protein-regulated apical Cl- channel exists in intestinal epithelial cells.
- This finding suggests an alternative regulatory pathway for transepithelial salt transport.
- This pathway may offer insights into anomalous channel regulation seen in cystic fibrosis.