期刊
JOURNAL OF PHYSIOLOGY-LONDON
卷 582, 期 3, 页码 917-925出版社
WILEY-BLACKWELL
DOI: 10.1113/jphysiol.2007.132498
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资金
- MRC [G0500194] Funding Source: UKRI
- Medical Research Council [G0500194] Funding Source: researchfish
- Medical Research Council [G0500194] Funding Source: Medline
- Wellcome Trust Funding Source: Medline
M-channels are voltage-gated K(+) channels that regulate the excitability of many neurons. They are composed of Kv7 (KCNQ) family subunits, usually Kv7.2 + Kv7.3. Native M-channels and expressed Kv7.2 + 7.3 channels are inhibited by stimulating G(q/11)-coupled receptors - prototypically the M1 muscarinic acetylcholine receptor (M1-mAChR). The channels require membrane phosphatidylinositol-4,5-bisphosphate (PIP(2)) to open and the effects of mAChR stimulation result primarily from the reduction in membrane PIP(2) levels following G(q)/phospholipase C-catalysed PIP(2) hydrolysis. However, in sympathetic neurons, M-current inhibition by bradykinin appears to be mediated through the release and action of intracellular Ca(2+) by inositol-1,4,5-trisphosphate (IP(3)), a product Of PIP(2) hydrolysis, rather than by PIP(2) depletion. We have therefore compared the effects of bradykinin and oxotremorine-M (a muscarinic agonist) on membrane PIP(2) in sympathetic neurons using a fluorescently tagged mutated C-domain of the PIP(2) binding probe, 'tubby'. In concentrations producing equal M-current inhibition, bradykinin produced about one-quarter of the reduction in PIP(2) produced by oxotremorine-M, but equal reduction when PIP(2) Synthesis was blocked with wortmannin. Likewise, wortmannin restored bradykinin-induced M-current inhibition when Ca(2+) release was prevented with thapsigargin. Thus, inhibition by bradykinin can use product (IP(3)/Ca(2+))-dependent or substrate (PIP(2)) dependent mechanisms, depending on Ca(2+) availability and PIP(2) synthesis rates.
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