AJP - Cell Physiology, Vol 263, Issue 3 C607-C615, Copyright © 1992 by American Physiological Society
Stimulation of intestinal Cl- transport by heat-stable enterotoxin: activation of cAMP-dependent protein kinase by cGMP
L. R. Forte, P. K. Thorne, S. L. Eber, W. J. Krause, R. H. Freeman, S. H. Francis and J. D. Corbin
Department of Pharmacology, Missouri University School of Medicine, Columbia.
Heat-stable enterotoxins activate guanylate cyclase, whereas heat-labile
enterotoxins stimulate adenylate cyclase. Both classes of toxins cause
secretory diarrhea at least in part by stimulating Cl- secretion in the
intestine. The mechanism for regulation of Cl- secretion by guanosine
3',5'-cyclic monophosphate (cGMP) was investigated using cultured T84
intestinal cells as a model for intestinal crypt cells. Escherichia coli
heat-stable enterotoxin (ST) markedly stimulated cGMP production in T84
cells. Cl- secretion across T84 cell monolayers cultured on permeable
filters was stimulated by E. coli ST, cholera toxin, or 8-BrcAMP, but
8-BrcGMP was ineffective. cGMP analogues that are known to be potent and
specific activators of cGMP-dependent protein kinase (cG-kinase) also had
little effect on 36Cl- uptake by T84 cells cultured in plastic dishes. E.
coli ST, forskolin, cholera toxin, or membrane-permeant cAMP analogues
markedly increased 36Cl- uptake into T84 cells. The general protein kinase
inhibitor, staurosporine, inhibited the stimulation of Cl- permeability
elicited by E. coli ST, vasoactive intestinal peptide (VIP), or 8-BrcAMP.
DEAE-Sephacel chromatography revealed a predominant type II isoform of
cAMP-dependent protein kinase (cA-kinase) in T84 cells, whereas little or
no cytosolic cG-kinase activity was found. Treatment of T84 cells with E.
coli ST or VIP resulted in an increase in the cA-kinase activity ratio
(-cAMP/+cAMP) if the cytosolic enzyme was assayed at reduced temperature
(on ice).(ABSTRACT TRUNCATED AT 250 WORDS)
