G-proteins mediate intestinal chloride channel activation.

Abstract

The localization of several GTP-binding regulatory proteins in teh apical membrane of intestinal epithelial cells has prompted us to investigate a possible role for G-proteins as modulators of apical Cl- channels. In membrane vesicles isolated from rat small intestine or human HT29-cl.19A colon carcinoma cells, the entrapment of guanosine 5'-O-(3-thiophosphate (GTP gamma S) led to a large increase in Cl- conductance, as evidenced by an increased 125I- uptake and faster SPQ quenching. The enhancement was observed in the presence, but not in the absence of the K+ ionophore valinomycin, indicating that the increased Cl- permeability is not secondary to the opening of K+ channels. The effect of GTP gamma S was counteracted by guanosine 5'-O-(2-thiophosphate (GDP beta S) and appeared to be independent of cytosolic messengers, including ATP, cAMP, and Ca2+, suggesting that protein phosphorylation and/or phospholipase C activation is not involved. Patch clamp analysis of apical membrane patches of HT29-cl.19A colonocytes revealed a GTP gamma S-activated, inwardly rectifying, anion-selective channel with a unitary conductance of 20 +/- 4 pS. No spontaneous channel openings were observed in the absence of GTP gamma S, while the open time probability (Po) increases dramatically to 0.81 +/- 0.09 upon addition with GTP gamma S. Since the electrophysiological characteristics and regulatory properties of this channel are markedly different from those of the more widely studied cAMP/protein kinase A-operated channel, we propose the existence of a separate Cl(-)-selective ion channel in the apical border of intestinal epithelial cells. Our results suggest an alternative regulatory pathway in transepithelial salt transport and a possible site for anomalous channel regulation as observed in cystic fibrosis patients.

• Authors: B C Tilly, M Kansen, P G van Gageldonk, N van den Berghe, H Galjaard, J Bijman, H R de Jonge
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 266 Issue 4 Pg. 2036-40 (Feb 05 1991) ISSN: 0021-9258 [Print] United States
• PMID: 1703525 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Chloride Channels
• Chlorides
• Ion Channels
• Membrane Proteins
• Potassium Channels
• Valinomycin
• Guanosine 5'-O-(3-Thiotriphosphate)
• GTP-Binding Proteins

Topics

• Animals
• Cell Membrane (metabolism)
• Chloride Channels
• Chlorides (metabolism)
• Colonic Neoplasms
• Epithelium (metabolism)
• GTP-Binding Proteins (metabolism)
• Guanosine 5'-O-(3-Thiotriphosphate) (metabolism, pharmacology)
• Humans
• Intestinal Mucosa (metabolism)
• Ion Channels (metabolism)
• Kinetics
• Membrane Proteins (metabolism)
• Potassium Channels (metabolism)
• Rats
• Tumor Cells, Cultured
• Valinomycin (pharmacology)