Multiple P2Y receptor subtypes in the apical membranes of polarized epithelial cells

H. L McAlroy, S. Ahmed, S. M. Day, D. L. Baines, H. Y. Wong, C. Y. Yip, W. H. Ko, S. M. Wilson, A. Collett

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Abstract

1. Apical ATP, UTP and UDP evoked transient increases in short circuit current (ISC, a direct measure of transepithelial ion transport) in confluent Caco-2 cells grown on permeable supports. These responses were mediated by a population of at least three pharmacologically distinct receptors. 

2. Experiments using cells grown on glass coverslips showed that ATP and UTP consistently increased intracellular free calcium ([Ca2+]i) whilst sensitivity to UDP was variable. Cross desensitization experiments suggested that the responses to UTP and ATP were mediated by a common receptor population. 

3. Messenger RNA transcripts corresponding to the P2Y2, P2Y4 and P2Y6 receptors genes were detected in cells grown on Transwell membranes by the reverse transcriptase-polymerase chain reaction. Identical results were obtained for cells grown on glass. 

4. Experiments in which ISC and [Ca2+]i were monitored simultaneously in cells on Transwell membranes, confirmed that apical ATP and UTP increased both parameters and showed that the UDP-evoked increase in ISC was accompanied by a [Ca2+]i-signal. 

5. Ionomycin consistently increased [Ca2+]i in such polarized cells but caused no discernible change in ISC. However, subsequent application of apical ATP or UTP evoked a small rise in ISC but no rise in [Ca2+]i. UDP evoked no such response. 

6. As well as evoking increases in [Ca2+]i, the ATP/UTP-sensitive receptors present in Caco-2 cells thus allow direct control over ion channels in the apical membrane. The UDP-sensitive receptors, however, appear to simply evoke a rise in [Ca2+]i.

Original languageEnglish
Pages (from-to)1651-1658
Number of pages8
JournalBritish Journal of Pharmacology
Volume131
Issue number8
DOIs
Publication statusPublished - Dec 2000
Externally publishedYes

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