Regulation of M(Kv7.2/7.3) channels in neurons by PIP(2) and products of PIP(2) hydrolysis: significance for receptor-mediated inhibition.
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.
Brown
David A
DA
Department of Pharmacology, University College London, London, WC1E 6BT, UK. d.a.brown@ucl.ac.uk
Hughes
Simon A
SA
Marsh
Stephen J
SJ
Tinker
Andrew
A
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D006868:Hydrolysis; D051658:KCNQ2 Potassium Channel / Q000502:physiology*; D051659:KCNQ3 Potassium Channel / Q000502:physiology*; D009116:Muscarine / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D011898:Ranidae; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D019269:Phosphatidylinositol 4,5-Diphosphate; D011976:Receptors, Muscarinic; D019284:Thapsigargin; D009116:Muscarine; D000077191:Wortmannin