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1 Dalton Cardiovascular Research Center and Department of Veterinary Biomedical Sciences and Departments of 3 Biochemistry and 4 Pharmacology, University of Missouri-Columbia, Columbia, Missouri 65211; and 2 Department of Chemistry, University of Puerto Rico, Río Piedras, Puerto Rico 00931
Desensitization of
P2Y2 receptor-activated anion
secretion may limit the usefulness of extracellular nucleotides in
secretagogue therapy of epithelial diseases, e.g., cystic fibrosis
(CF). To investigate the desensitization process for endogenous
P2Y2 receptors, freshly excised or
cultured murine gallbladder epithelia (MGEP) were mounted in Ussing
chambers to measure short-circuit current (Isc), an index
of electrogenic anion secretion. Luminal treatment with nucleotide
receptor agonists increased the
Isc with a
potency profile of ATP = UTP > 2-methylthioATP >>
,
-methylene-ATP. RT-PCR revealed the expression of
P2Y2 receptor mRNA in the MGEP
cells. The desensitization of anion secretion required a 10-min
preincubation with the P2Y2
receptor agonist UTP and increased in a
concentration-dependent manner
(IC50
10
6 M). Approximately 40%
of the anion secretory response was unaffected by maximal desensitizing
concentrations of UTP. Recovery from UTP-induced desensitization was
rapid (<10 min) at preincubation concentrations less than the
EC50 (1.9 × 10
6 M) but required
progressively longer time periods at greater concentrations.
UTP-induced total inositol phosphate production and intracellular
Ca2+ mobilization desensitized
with a concentration dependence similar to that of anion secretion. In
contrast, maximal anion secretion induced by
Ca2+ ionophore ionomycin was
unaffected by preincubation with a desensitizing concentration of UTP.
It was concluded that 1)
desensitization of transepithelial anion secretion stimulated by the
P2Y2 receptor agonist UTP is time
and concentration dependent; 2)
recovery from desensitization is prolonged (>90 min) at UTP
concentrations >10
5 M;
and 3) UTP-induced desensitization
occurs before the operation of the anion secretory mechanism.
receptor regulation; chloride secretion; bicarbonate secretion; cystic fibrosis; mouse; gallbladder; epithelium
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