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Novel consequences of voltage‐dependence to G‐protein‐coupled P2Y 1 receptors
Author(s) -
Gurung I S,
MartinezPinna J,
MahautSmith M P
Publication year - 2008
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/bjp.2008.97
Subject(s) - depolarization , agonist , biophysics , receptor , allosteric regulation , g protein coupled receptor , chemistry , membrane potential , allosteric modulator , inverse agonist , partial agonist , pharmacology , biology , biochemistry
Background and purpose: Emerging evidence suggests that activation of G‐protein‐coupled receptors (GPCRs) can be directly regulated by membrane voltage. However, the physiological and pharmacological relevance of this effect remains unclear. We have further examined this phenomenon for P2Y 1 receptors in the non‐excitable megakaryocyte using a range of agonists and antagonists. Experimental approach: Simultaneous whole‐cell patch clamp and fura‐2 fluorescence recordings of rat megakaryocytes, which lack voltage‐gated Ca 2+ influx, were used to examine the voltage‐dependence of P2Y 1 receptor‐evoked IP 3 ‐dependent Ca 2+ mobilization. Results: Depolarization transiently and repeatedly enhanced P2Y 1 receptor‐evoked Ca 2+ mobilization across a wide concentration range of both weak, partial and full, potent agonists. Moreover, the amplitude of the depolarization‐evoked [Ca 2+ ] i increase displayed an inverse relationship with agonist concentration, such that the greatest potentiating effect of voltage was observed at near‐threshold levels of agonist. Unexpectedly, depolarization also stimulated an [Ca 2+ ] i increase in the absence of agonist during exposure to the competitive antagonists A3P5PS and MRS2179, or the allosteric enhancer 2,2′‐pyridylisatogen tosylate. A further effect of some antagonists, particularly suramin, was to enhance the depolarization‐evoked Ca 2+ responses during co‐application of an agonist. Of several P2Y 1 receptor inhibitors, only SCH202676, which has a proposed allosteric mechanism of action, could block ADP‐induced voltage‐dependent Ca 2+ release. Conclusions and implications: The ability of depolarization to potentiate GPCRs at near‐threshold agonist concentrations represents a novel mechanism for coincidence detection. Furthermore, the induction and enhancement of voltage‐dependent GPCR responses by antagonists has implications for the design of therapeutic compounds. British Journal of Pharmacology (2008) 154 , 882–889; doi: 10.1038/bjp.2008.97 ; published online 14 April 2008