Lukacs Viktor, Thyagarajan Baskaran, Varnai Peter, Balla Andras, Balla Tamas, Rohacs Tibor
Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103, USA.
J Neurosci. 2007 Jun 27;27(26):7070-80. doi: 10.1523/JNEUROSCI.1866-07.2007.
The membrane phospholipid phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2 or PIP2] regulates many ion channels. There are conflicting reports on the effect of PtdIns(4,5)P2 on transient receptor potential vanilloid 1 (TRPV1) channels. We show that in excised patches PtdIns(4,5)P2 and other phosphoinositides activate and the PIP2 scavenger poly-Lys inhibits TRPV1. TRPV1 currents undergo desensitization on exposure to high concentrations of capsaicin in the presence of extracellular Ca2+. We show that in the presence of extracellular Ca2+, capsaicin activates phospholipase C (PLC) in TRPV1-expressing cells, inducing depletion of both PtdIns(4,5)P2 and its precursor PtdIns(4)P (PIP). The PLC inhibitor U73122 and dialysis of PtdIns(4,5)P2 or PtdIns(4)P through the patch pipette inhibited desensitization of TRPV1, indicating that Ca2+-induced activation of PLC contributes to desensitization of TRPV1 by depletion of PtdIns(4,5)P2 and PtdIns(4)P. Selective conversion of PtdIns(4,5)P2 to PtdIns(4)P by a rapamycin-inducible PIP2 5-phosphatase did not inhibit TRPV1 at high capsaicin concentrations, suggesting a significant role for PtdIns(4)P in maintaining channel activity. Currents induced by low concentrations of capsaicin and moderate heat, however, were potentiated by conversion of PtdIns(4,5)P2 to PtdIns(4)P. Increasing PtdIns(4,5)P2 levels by coexpressing phosphatidylinositol-4-phosphate 5-kinase inhibited TRPV1 at low but not at saturating capsaicin concentrations. These data show that at low capsaicin concentrations and other moderate stimuli, PtdIns(4,5)P2 partially inhibits TRPV1 in a cellular context, but this effect is likely to be indirect, because it is not detectable in excised patches. We conclude that phosphoinositides have both inhibitory and activating effects on TRPV1, resulting in complex and distinct regulation at various stimulation levels.
膜磷脂磷脂酰肌醇4,5 - 二磷酸[PtdIns(4,5)P2或PIP2]调节多种离子通道。关于PtdIns(4,5)P2对瞬时受体电位香草酸受体1（TRPV1）通道的影响，存在相互矛盾的报道。我们发现，在切除的膜片中，PtdIns(4,5)P2和其他磷酸肌醇可激活TRPV1，而PIP2清除剂聚赖氨酸则抑制TRPV1。在细胞外Ca2+存在的情况下，暴露于高浓度辣椒素时，TRPV1电流会发生脱敏。我们发现，在细胞外Ca2+存在的情况下，辣椒素可激活表达TRPV1的细胞中的磷脂酶C（PLC），导致PtdIns(4,5)P2及其前体PtdIns(4)P（PIP）均被耗尽。PLC抑制剂U73122以及通过膜片电极对PtdIns(4,5)P2或PtdIns(4)P进行透析可抑制TRPV1的脱敏，这表明Ca2+诱导的PLC激活通过耗尽PtdIns(4,5)P2和PtdIns(4)P导致TRPV1脱敏。雷帕霉素诱导的PIP2 5 - 磷酸酶将PtdIns(4,5)P2选择性转化为PtdIns(4)P，在高浓度辣椒素条件下并未抑制TRPV1，这表明PtdIns(4)P在维持通道活性方面具有重要作用。然而，低浓度辣椒素和适度热诱导的电流在PtdIns(4,5)P2转化为PtdIns(4)P后增强。通过共表达磷脂酰肌醇 - 4 - 磷酸5 - 激酶增加PtdIns(4,5)P2水平，在低浓度但非饱和辣椒素浓度下抑制TRPV1。这些数据表明，在低浓度辣椒素和其他适度刺激下，PtdIns(4,5)P2在细胞环境中部分抑制TRPV1，但这种作用可能是间接的，因为在切除的膜片中无法检测到。我们得出结论，磷酸肌醇对TRPV1具有抑制和激活作用，在不同刺激水平下导致复杂且独特的调节。
