Vedernikova E A, Maksimov A V, Neguliaev Iu A
Institute of Cytology, Russian Academy of Sciences, St. Petersburg.
Tsitologiia. 1997;39(12):1142-51.
The paper is devoted to membrane mechanisms of sodium influx from the extracellular medium to the cytoplasm in nonexcitable cells. With the use of patch clamp technique, the activity of non-voltage-gated ionic channels in plasma membrane of human leukemia K562 cells was examined. We have identified two types of Na-permeable channels characterized by unitary conductance of 12 pS and differing in their selectivity among monovalent cations. A relative permeability value PNa/PK was estimated for both types referred to as channels of high (HS, PNa/PK = 10) and low (LS, PNa/PK = 3) selectivity, resp. Both the channels were impermeable to bivalent cations (Ca2+, Ba2+), not blocked by tetradotoxin. Their sensitivity to amiloride was extremely low. Cytochalasin D treatment of cells resulted in a significant increase in the activity of LS Na-conducting channels. Application of exogenous gelsolin to the cytoplasmic surface of inside-out membrane patch at free Ca2+ level of 1 mkM induced a similar effect of sodium channel activation; the subsequent addition of actin reduced the channel activity up to the background level. Our results show that the cortical F-actin network plays an important role in regulating the novel family of sodium channels in nonexcitable cells. It could be assumed that the actin disassembly causes a rise in LS channel activity, whereas the actin assembly induces inactivation of the channels.
本文致力于研究非兴奋性细胞中钠离子从细胞外介质流入细胞质的膜机制。运用膜片钳技术，检测了人白血病K562细胞质膜上非电压门控离子通道的活性。我们鉴定出两种类型的钠通透通道，其单通道电导为12 pS，对单价阳离子的选择性不同。分别估算了这两种类型通道的相对通透性值PNa/PK，分别称为高选择性通道（HS，PNa/PK = 10）和低选择性通道（LS，PNa/PK = 3）。这两种通道都不能通透二价阳离子（Ca2+、Ba2+），不受河豚毒素的阻断。它们对氨氯吡咪的敏感性极低。用细胞松弛素D处理细胞会导致LS钠传导通道的活性显著增加。在游离Ca2+水平为1 mkM时，将外源性凝溶胶蛋白应用于内翻膜片的细胞质表面会诱导类似的钠通道激活效应；随后添加肌动蛋白会使通道活性降低至背景水平。我们的结果表明，皮质F-肌动蛋白网络在调节非兴奋性细胞中新型钠通道家族方面起着重要作用。可以推测，肌动蛋白解聚导致LS通道活性升高，而肌动蛋白组装则诱导通道失活。
