Modulation of Cl- secretion in rat distal colon by genistein, a protein tyrosine kinase inhibitor.
The protein tyrosine kinase inhibitor, genistein, caused an increase of short-circuit current (Isc) across the rat distal colon in forskolin-pretreated tissues, suggesting a synergistic interaction of the drug with cAMP-dependent secretion. In the absence of forskolin, genistein had a dual effect on Isc, it increased Isc in tissues with a low baseline, but decreased Isc in tissues with a high baseline Isc. The secretory effect of genistein was dependent on the presence of Cl- and was blocked by inhibitors of Cl- secretion like bumetanide, an inhibitor of the Na(+)-K(+)-Cl- cotransporter, or 5-nitro-2-(3- phenylpropylamino)-benzoate (NPPB), a Cl- channel blocker. Unidirectional flux measurements revealed that genistein inhibited Na+ and Cl- absorption and induced net Cl- secretion. The protein tyrosine phosphatase inhibitor vanadate suppressed the secretory effect of genistein. In contrast, genistein caused an inhibition of carbachol-induced, i.e. Ca(2+)-mediated secretion. Whole-cell patch-clamp experiments confirmed the synergistic effect of genistein on cAMP-induced Cl- currents. In the presence of forskolin, genistein caused a depolarization concomitant with an increase in membrane inward current. In addition, genistein caused an inhibition of a basal K+ conductance and inhibited the Ca(2+)-dependent K+ conductance stimulated by carbachol. These results suggest a complex role of the protein tyrosine kinase pathway in the control of colonic Cl- secretion, an antagonistic action on the cAMP pathway and a synergistic action on the Ca2+ pathway as revealed by the opposing effects of genistein. The physiological importance of this regulation remains to be clarified.
Institut für Veterinär-Physiologie, Justus-Liebig-Universität Giessen, Germany.
M
M
Diener
F
F
Hug
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D019833:Genistein; D066298:In Vitro Techniques; D007529:Isoflavones / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D051381:Rats
D002712:Chlorides; D004791:Enzyme Inhibitors; D007529:Isoflavones; D005576:Colforsin; D002217:Carbachol; D019833:Genistein; D011505:Protein-Tyrosine Kinases