Starkus John G, Varga Zoltan, Schönherr Roland, Heinemann Stefan H
PBRC, Bekesy Laboratory of Neurobiology, University of Hawaii, Honolulu, Hawaii 96822, USA.
Pflugers Arch. 2003 Oct;447(1):44-54. doi: 10.1007/s00424-003-1121-0. Epub 2003 Aug 12.
Potassium channels are regulated by protons in various ways and, in most cases, acidification results in potassium current reduction. To elucidate the mechanisms of proton-channel interactions we investigated N-terminally truncated Shaker potassium channels (Kv1 channels) expressed in Xenopus oocytes, varying pH at the intracellular and the extracellular face of the membrane. Intracellular acidification resulted in rapid and reversible channel block. The block was half-maximal at pH 6.48, thus even physiological excursions of intracellular pH will have an impact on K+ current. The block displayed only very weak voltage dependence and C-type inactivation and activation were not affected. Extracellular acidification (up to pH 4) did not block the channel, indicating that protons are effectively excluded from the selectivity filter. Channel current, however, was reduced greatly due to marked acceleration of C-type inactivation at low pH. In contrast, inactivation was not affected in the T449V mutant channel, in which C-type inactivation is impaired. The pH effect on inactivation of the wild-type channel had an apparent pK of 4.7, suggesting that protonation of extracellular acidic residues in Kv channels makes them subject to pH regulation.
钾通道受质子以多种方式调控，在大多数情况下，酸化会导致钾电流减少。为阐明质子与通道相互作用的机制，我们研究了在非洲爪蟾卵母细胞中表达的N端截短的Shaker钾通道（Kv1通道），改变膜内、外表面的pH值。细胞内酸化导致通道快速且可逆的阻断。该阻断在pH 6.48时达到半数最大效应，因此即使细胞内pH值的生理性波动也会对钾电流产生影响。该阻断仅表现出非常微弱的电压依赖性，且C型失活和激活不受影响。细胞外酸化（至pH 4）并未阻断通道，这表明质子被有效地排除在选择性过滤器之外。然而，由于在低pH值下C型失活明显加速，通道电流大幅降低。相比之下，在T449V突变通道中失活不受影响，该突变通道的C型失活受损。野生型通道失活的pH效应的表观pK值为4.7，这表明Kv通道中细胞外酸性残基的质子化使其受到pH调控。
