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CELLULAR |
1 Ion Channels and Cell Signalling, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London SW17 ORE, UK
In the present work we used patch pipette techniques to study the properties of a novel Ca2+-permeable cation channel activated by the potent coronary vasoconstrictor endothelin-1 (ET-1) in freshly dispersed rabbit coronary artery myocytes. With cell-attached recording bath application of 10 nM ET-1 evoked cation channel currents (Icat) with subconductance states of about 18, 34 and 51 and 68 pS, and a reversal potential of 0 mV. ET-1 evoked channel activity when extracellular Ca2+ was the charge carrier, illustrating significant Ca2+ permeability. ET-1-induced responses were inhibited by the ETA receptor antagonist BQ123 and the phospholipase C (PLC) inhibitor U73122. The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) also stimulated Icat, but the protein kinase C (PKC) inhibitor chelerythrine did not inhibit either the OAG- or ET-1-induced Icat. Inositol 1,4,5-trisphosphate (IP3) did not activate Icat, but greatly potentiated the response to OAG and this effect was blocked by heparin. Bath application of anti-TRPC3 and anti-TRPC7 antibodies to inside-out patches markedly inhibited ET-1-evoked Icat, but antibodies to TRPC1, C4, C5 and C6 had no effect. Immunocytochemical studies demonstrated preferential TRPC7 expression in the plasmalemma, whereas TRPC3 was distributed throughout the myocyte, and moreover co-localization of TRPC3 and TRPC7 signals was observed at, or close to, the plasma membrane. Flufenamic acid, Gd3+, La3+ and extracellular Ca2+ inhibited Icat with IC50 values of 2.45 µM, 3.8 µM, 7.36 µM and 22 µM, respectively. These results suggest that in rabbit coronary artery myocytes ET-1 evokes a Ca2+-permeable non-selective cation channel with properties similar to TRPC3 and TRPC7, and indicates that these proteins may be important components of this conductance.
(Received 14 December 2006;
accepted after revision 15 February 2007;
first published online 15 February 2007)
Corresponding author A. P. Albert: Ion Channel and Cell Signalling, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London SW17 ORE, UK. Email: aalbert{at}sgul.ac.uk
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