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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Phosphatidylinositol 4,5-bisphosphate hydrolysis mediates histamine-induced KCNQ/M current inhibition

Department of Pharmacology, Hebei Medical University, Shijiazhuang, Hebei Province, China

Submitted 22 January 2008 ; accepted in final form 27 April 2008

The M-type potassium channel, of which its molecular basis is constituted by KCNQ2-5 homo- or heteromultimers, plays a key role in regulating neuronal excitability and is modulated by many G protein-coupled receptors. In this study, we demonstrate that histamine inhibits KCNQ2/Q3 currents in human embryonic kidney (HEK)293 cells via phosphatidylinositol 4,5-bisphosphate (PIP₂) hydrolysis mediated by stimulation of H₁ receptor and phospholipase C (PLC). Histamine inhibited KCNQ2/Q3 currents in HEK293 cells coexpressing H₁ receptor, and this effect was totally abolished by H₁ receptor antagonist mepyramine but not altered by H₂ receptor antagonist cimetidine. The inhibition of KCNQ currents was significantly attenuated by a PLC inhibitor U-73122 but not affected by depletion of internal Ca²⁺ stores or intracellular Ca²⁺ concentration ([Ca²⁺]_i) buffering via pipette dialyzing BAPTA. Moreover, histamine also concentration dependently inhibited M current in rat superior cervical ganglion (SCG) neurons by a similar mechanism. The inhibitory effect of histamine on KCNQ2/Q3 currents was entirely reversible but became irreversible when the resynthesis of PIP₂ was impaired with phosphatidylinsitol-4-kinase inhibitors. Histamine was capable of producing a reversible translocation of the PIP₂ fluorescence probe PLC₁-PH-GFP from membrane to cytosol in HEK293 cells by activation of H₁ receptor and PLC. We concluded that the inhibition of KCNQ/M currents by histamine in HEK293 cells and SCG neurons is due to the consumption of membrane PIP₂ by PLC.

superior cervical ganglion; phosphatidylinositol 4,5-bisphosphate; calcium ion