Heterotrimeric G-proteins activate Cl- channels through stimulation of a cyclooxygenase-dependent pathway in a model liver cell line.
Circulating hormones produce rapid changes in the Cl(-) permeability of liver cells through activation of plasma membrane receptors coupled to heterotrimeric G-proteins. The resulting effects on intracellular pH, membrane potential, and Cl(-) content are important contributors to the overall metabolic response. Consequently, the purpose of these studies was to evaluate the mechanisms responsible for G-protein-mediated changes in membrane Cl(-) permeability using HTC hepatoma cells as a model. Using patch clamp techniques, intracellular dialysis with 0.3 mm guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) increased membrane conductance from 10 to 260 picosiemens/picofarads due to activation of Ca(2+)-dependent Cl(-) currents that were outwardly rectifying and exhibited slow activation at depolarizing potentials. These effects were mimicked by intracellular AlF(4)(-) (0.03 mm) and inhibited by pertussis toxin (PTX), consistent with current activation through Galpha(i). Studies using defined agonists and inhibitors indicate that Cl(-) channel activation by GTPgammaS occurs through an indomethacin-sensitive pathway involving sequential activation of phospholipase C, mobilization of Ca(2+) from inositol 1,4,5-trisphosphate-sensitive stores, and stimulation of phospholipase A(2) and cyclooxygenase (COX). Accordingly, the conductance responses to GTPgammaS or to intracellular Ca(2+) were inhibited by COX inhibitors. These results indicate that PTX-sensitive G-proteins regulate the Cl(-) permeability of HTC cells through Ca(2+)-dependent stimulation of COX activity. Thus, receptor-mediated activation of Galpha(i) may be essential for hormonal regulation of liver transport and metabolism through COX-dependent opening of a distinct population of plasma membrane Cl(-) channels.
Kilic
Gordan
G
Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. gordan.kilic@uchsc.edu
Fitz
J Gregory
JG
D000255:Adenosine Triphosphate / Q000378:metabolism; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000737:chemistry* / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007213:Indomethacin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008954:Models, Biological; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D010741:Phospholipases A / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D018118:Chloride Channels; D010566:Virulence Factors, Bordetella; D016718:Arachidonic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D011451:Prostaglandin-Endoperoxide Synthases; D037342:Pertussis Toxin; D010741:Phospholipases A; D019204:GTP-Binding Proteins; D002118:Calcium; D009638:Norepinephrine; D007213:Indomethacin