G-proteins mediate intestinal chloride channel activation

B C Tilly,M Kansen,P G Van Gageldonk,N Van Den Berghe,H Galjaard,J Bijman,H R De Jonge

doi:10.1016/s0021-9258(18)52205-5

B C Tilly, M Kansen + Show 5 more

Open Access

https://doi.org/10.1016/s0021-9258(18)52205-5

Copy DOI

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.

Highlights

RESULTSIn an initial series of experiments, C1- channel activation drivingforceforprolonged lZ5I- accumulation (cf. Ref. 14). was studied ina suspension of KC1-loaded plasma membrane Second, the contribution of an additional subpopulation of vesicles obtained from human HT-29c1.19A cells, a C1"se- vesicles which accumulate Iz5I- solely inthe presence of creting subclone isolated from theoriginal HT-29 colon car- guanine nucleotides may give rise to a further increase in the cinoma cell line (17)
The localization of several GTP-binding regulatory structure of epithelial C1- channels (4), their mode of activaproteins in the apicalmembrane of intestinal epithelial tion hasbeen analyzed in more detail
In ers, Ussing chamber) several intracellular regulatory mechamembrane vesicles isolated from rat small intestine or human HT29-cl.lSA colon carcinoma cells, the entrapment of guanosine 5’-0-(3-thiophosphate (GTPyS) led to a large increasein Cl- conductance, as evidenced by an increased IZsI-uptake and faster SPQ quenching

Summary

RESULTS

In an initial series of experiments, C1- channel activation drivingforceforprolonged lZ5I- accumulation (cf. Ref. 14). was studied ina suspension of KC1-loaded plasma membrane Second, the contribution of an additional subpopulation of vesicles obtained from human HT-29c1.19A cells, a C1"se- vesicles which accumulate Iz5I- solely inthe presence of creting subclone isolated from theoriginal HT-29 colon car- guanine nucleotides may give rise to a further increase in the cinoma cell line (17). As expected by quantitating C1- diffusion potential-driven uptakeof tracer for right-side-out vesicles, no effects of GTPyS were observed amounts of radiolabeled iodine. We found this method supe- when added aftevr esicle resealing (not shown), demonstrating rior to "Cl- influx assays because: 1)epithelial anion channels that GTPyS acts on thceytoplasmic side of the membrane. Recent studhaievse revealed accumulated exclusively into intact vesicles containing func- that this water-soluble dye, whose fluorescence is quenched tional C1- channels (cf Ref. 14), resultingindiminished in the presence ofC1-, is a suitable and sensitive probe for background labeling andincreasedsensitivity. In the presence vesicles, suggesting that GTPySinduces a sustained increase of valinomycin, i.e. when generation of a counteracting mem-

Effects ofguanine nucleotides on SPQ quenching

GTPyS GTPyS

GTPyS GDPPS