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Department of Medicine, University of California, San Diego, School of Medicine, San Diego, California 92103
Our goal was to
examine the sidedness of effects of the purinergic agonist, uridine
5'-triphosphate (UTP), on Cl
secretion in intestinal
epithelial cells. We hypothesized that UTP might exert both stimulatory
and inhibitory effects. All studies were conducted with T84 intestinal
epithelial cells. UTP induced Cl
secretion in a
concentration-dependent fashion. Responses to serosally added UTP were
smaller and more transient than those evoked by mucosal addition, but
there was no evidence that mucosal responses involved cAMP-dependent
mechanisms. Pretreatment with serosal UTP inhibited subsequent
Ca2+-dependent Cl
secretion induced by
carbachol or thapsigargin, or secretion induced by mucosal UTP, in a
manner that was reversed by a tyrosine kinase inhibitor. The inhibitory
effect of serosal UTP on Cl
secretion was not additive
with that of carbachol, known to exert its inhibitory effects through
the tyrosine kinase-dependent generation of inositol
3,4,5,6-tetrakisphosphate
[Ins(3,4,5,6)P4]. Moreover, responses to both serosal and mucosal UTP were reduced by prior treatment of T84 cells with carbachol. Finally, serosal, but not mucosal, UTP evoked an increase in
Ins(3,4,5,6)P4. We conclude that
different signaling mechanisms lie downstream of apical and basolateral
UTP receptors in epithelial cells, at least in the intestine. These
differences may be relevant to the use of UTP as a therapy in cystic fibrosis.
intestine; calcium; uridine 5'-triphosphate; purinergic agonists
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