Tang X D, Hoshi T
Department of Physiology and Biophysics, The University of Iowa, Iowa City, Iowa 52242, USA.
Biophys J. 1999 Jun;76(6):3089-98. doi: 10.1016/S0006-3495(99)77461-8.
Disappearance of the functional activity or rundown of ion channels upon patch excision in many cells involves a decrease in the number of channels available to open. A variety of cellular and biophysical mechanisms have been shown to be involved in the rundown of different ion channels. We examined the rundown process of the plant hyperpolarization-activated KAT1 K+ channel expressed in Xenopus oocytes. The decrease in the KAT1 channel activity on patch excision was accompanied by progressive slowing of the activation time course, and it was caused by a shift in the voltage dependence of the channel without any change in the single-channel amplitude. The single-channel analysis showed that patch excision alters only the transitions leading up to the burst states of the channel. Patch cramming or concurrent application of protein kinase A (PKA) and ATP restored the channel activity. In contrast, nonspecific alkaline phosphatase (ALP) accelerated the rundown time course. Low internal pH, which inhibits ALP activity, slowed the KAT1 rundown time course. The results show that the opening transitions of the KAT1 channel are enhanced not only by hyperpolarization but also by PKA-mediated phosphorylation.
在许多细胞中，膜片钳切除后离子通道功能活性的消失或衰减涉及到可开放通道数量的减少。多种细胞和生物物理机制已被证明与不同离子通道的衰减有关。我们研究了在非洲爪蟾卵母细胞中表达的植物超极化激活的KAT1钾通道的衰减过程。膜片钳切除时KAT1通道活性的降低伴随着激活时程的逐渐减慢，这是由通道电压依赖性的改变引起的，而单通道幅度没有任何变化。单通道分析表明，膜片钳切除仅改变导致通道爆发状态的转换。膜片填充或同时应用蛋白激酶A（PKA）和ATP可恢复通道活性。相反，非特异性碱性磷酸酶（ALP）加速了衰减时程。抑制ALP活性的低胞内pH减缓了KAT1衰减时程。结果表明，KAT1通道的开放转换不仅通过超极化增强，还通过PKA介导的磷酸化增强。
