Guo Juan, Schofield Geoffery G
Department of Physiology, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
J Physiol. 2002 Dec 15;545(3):767-81. doi: 10.1113/jphysiol.2002.026583.
The M-type potassium current (I(M)) plays a dominant role in regulating membrane excitability and is modulated by many neurotransmitters. However, except in the case of bradykinin, the signal transduction pathways involved in M-channel modulation have not been fully elucidated. The channels underlying I(M) are produced by the coassembly of KCNQ2 and KCNQ3 channel subunits and can be expressed in heterologous systems where they can be modulated by several neurotransmitter receptors including histamine H(1) receptors. In HEK293T cells, histamine acting via transiently expressed H(1)R produced a strong inhibition of recombinant M-channels but had no overt effects on the voltage dependence or voltage range of I(M) activation. In addition, the modulation of I(M) by histamine was not voltage sensitive, whereas channel gating, particularly deactivation, was accelerated by histamine. Non-hydrolysable guanine nucleotide analogues (GDP-beta-S and GTP-gamma-S) and pertussis toxin (PTX) treatment demonstrated the involvement of a PTX-insensitive G protein in the signal transduction pathway mediating histamine-induced I(M) modulation. Abrogation of the histamine-induced modulation of I(M) by expression of a C-terminal construct of phospholipase C (PLC-beta1-ct), which buffers activated Galpha(q/11) subunits, implicates this G protein alpha subunit in the modulatory pathway. On the other hand, abrogation of the histamine-induced modulation of I(M) by expression of two constructs which buffer free betagamma subunits, transducin (Galphat) and a C-terminal construct of a G protein receptor kinase (MAS-GRK2-ct), implicates betagamma dimers in the modulatory pathway. These findings demonstrate that histamine modulates recombinant M-channels in HEK293T cells via a PTX-insensitive G protein, probably Galpha(q/11), in a similar manner to a number of other G protein-coupled receptors. However, histamine-induced I(M) modulation in HEK293T cells is novel in that betagamma subunits in addition to Galpha(q/11) subunits appear to be involved in the modulation of KCNQ2/3 channel currents.
M 型钾电流（I(M)）在调节膜兴奋性方面起主导作用，并受多种神经递质调节。然而，除了缓激肽的情况外，参与 M 通道调节的信号转导途径尚未完全阐明。I(M) 的基础通道由 KCNQ2 和 KCNQ3 通道亚基共同组装产生，并且可以在异源系统中表达，在该系统中它们可被包括组胺 H(1) 受体在内的多种神经递质受体调节。在 HEK293T 细胞中，通过瞬时表达的 H(1)R 起作用的组胺对重组 M 通道产生强烈抑制，但对 I(M) 激活的电压依赖性或电压范围没有明显影响。此外，组胺对 I(M) 的调节不具有电压敏感性，而通道门控，特别是失活，被组胺加速。不可水解的鸟嘌呤核苷酸类似物（GDP-β-S 和 GTP-γ-S）和百日咳毒素（PTX）处理表明，一种对 PTX 不敏感的 G 蛋白参与了介导组胺诱导的 I(M) 调节的信号转导途径。通过表达磷脂酶 C（PLC-β1-ct）的 C 末端构建体消除组胺诱导的 I(M) 调节，该构建体缓冲活化的 Gα(q/11) 亚基，这表明该 G 蛋白α亚基参与调节途径。另一方面，通过表达两种缓冲游离βγ亚基的构建体，转导素（Gαt）和 G 蛋白受体激酶的 C 末端构建体（MAS-GRK2-ct）消除组胺诱导的 I(M) 调节，这表明βγ二聚体参与调节途径。这些发现表明，组胺通过一种对 PTX 不敏感的 G 蛋白，可能是 Gα(q/11)，以与许多其他 G 蛋白偶联受体类似的方式调节 HEK293T 细胞中的重组 M 通道。然而，组胺在 HEK293T 细胞中诱导的 I(M) 调节是新颖的，因为除了 Gα(q/11) 亚基之外，βγ亚基似乎也参与了 KCNQ2/3 通道电流的调节。
