title: Multiple P2Y receptor subtypes in the apical membranes of polarized epithelial cells.
abstract: Apical ATP, ATP, UTP and UDP evoked transient increases in short circuit current (I(SC), 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. Experiments using cells grown on glass coverslips showed that ATP and UTP consistently increased intracellular free calcium ([Ca(2+)](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. Messenger RNA transcripts corresponding to the P2Y(2), P2Y(4) and P2Y(6) 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. Experiments in which I(SC) and [Ca(2+)](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 I(SC) was accompanied by a [Ca(2+)](i)-signal. Ionomycin consistently increased [Ca(2+)](i) in such polarized cells but caused no discernible change in I(SC). However, subsequent application of apical ATP or UTP evoked a small rise in I(SC) but no rise in [Ca(2+)](i). UDP evoked no such response. As well as evoking increases in [Ca(2+)](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 [Ca(2+)](i).
authors.affiliation: Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY.
authors.forename: H L
authors.initials: HL
authors.lastname: McAlroy
authors.forename: S
authors.initials: S
authors.lastname: Ahmed
authors.forename: S M
authors.initials: SM
authors.lastname: Day
authors.forename: D L
authors.initials: DL
authors.lastname: Baines
authors.forename: H Y
authors.initials: HY
authors.lastname: Wong
authors.forename: C Y
authors.initials: CY
authors.lastname: Yip
authors.forename: W H
authors.initials: WH
authors.lastname: Ko
authors.forename: S M
authors.initials: SM
authors.lastname: Wilson
authors.forename: A
authors.initials: A
authors.lastname: Collett
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D018938:Caco-2 Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D058473:Receptors, Purinergic P2Y2; D014158:Transcription, Genetic; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: C546385:P2RY2 protein, human; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058473:Receptors, Purinergic P2Y2; C104749:purinoceptor P2Y4; C099845:purinoceptor P2Y6; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate