Lewis R S, Cahalan M D
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305, USA.
Annu Rev Immunol. 1995;13:623-53. doi: 10.1146/annurev.iy.13.040195.003203.
Over the past decade, a variety of ion channels have been identified and characterized in lymphocytes by use of the patch-clamp technique. This review discusses biophysical and regulatory aspects of lymphocyte potassium and calcium channels with the aim of understanding the role of these channels in lymphocyte functions. Lymphocytes express both voltage-dependent potassium [K(V)] channels and calcium-activated potassium [K(Ca)] channels, and each is upregulated as cells progress toward division following mitogenic stimulation. The genes encoding two K(V) channels, Kv1.3 (type n) and Kv3.1 (type l), have been cloned. Mutational analysis is revealing functionally important regions of these channel proteins. Exogenous expression studies and the use of highly specific channel blockers have helped to establish the roles of type n K(V) channels in sustaining the resting membrane potential, in regulating cell volume, and in enabling lymphocyte activation. Blockade of K(V) and K(Ca) channels effectively inhibits the antigen-driven activation of lymphocytes, probably by inducing membrane depolarization and thereby diminishing calcium influx. A prolonged rise in intracellular calcium ([Ca2+]i) is a required signal for lymphocyte activation by antigen or mitogens. Single-cell fluorescence measurements have revealed underlying [Ca2+]i oscillations that are linked closely to the opening and closing of Ca2+ and K+ channels. Sustained Ca2+ signaling and oscillations depend absolutely on plasma-membrane Ca2+ channels that are activated by the depletion of intracellular calcium stores. Under physiological conditions these channels open as a consequence of store depletion induced by inositol 1,4,5-trisphosphate (IP3), but they can also be activated experimentally by several agents that empty the stores without generating IP3, such as the microsomal Ca(2+)-ATPase inhibitor thapsigargin. The intricate causal relationships among ion channels, membrane potential, [Ca2+]i, and lymphokine gene expression can now be pursued at the single-cell level with patch-clamp recording, calcium-dependent dyes, reporter genes, and fluorescence video techniques. These approaches will help to clarify the essential roles of ion channels in the molecular pathways subserving activation and other lymphocyte behaviors.
在过去十年中，通过膜片钳技术在淋巴细胞中鉴定并表征了多种离子通道。本综述讨论淋巴细胞钾通道和钙通道的生物物理及调节方面，目的是了解这些通道在淋巴细胞功能中的作用。淋巴细胞表达电压依赖性钾通道（K(V)）和钙激活钾通道（K(Ca)），并且随着细胞在有丝分裂原刺激后向分裂进展，每种通道都会上调。编码两种K(V)通道Kv1.3（n型）和Kv3.1（l型）的基因已被克隆。突变分析正在揭示这些通道蛋白的功能重要区域。外源表达研究以及使用高度特异性的通道阻滞剂有助于确定n型K(V)通道在维持静息膜电位、调节细胞体积以及使淋巴细胞活化方面的作用。阻断K(V)和K(Ca)通道可有效抑制抗原驱动的淋巴细胞活化，这可能是通过诱导膜去极化从而减少钙内流来实现的。细胞内钙（[Ca2+]i）的持续升高是抗原或有丝分裂原激活淋巴细胞所需的信号。单细胞荧光测量揭示了与Ca2+和K+通道的开放和关闭密切相关的潜在[Ca2+]i振荡。持续的Ca2+信号传导和振荡绝对依赖于由细胞内钙库耗竭激活的质膜钙通道。在生理条件下，这些通道由于肌醇1,4,5-三磷酸（IP3）诱导的库耗竭而开放，但它们也可以通过几种不产生IP3而排空库的试剂进行实验性激活，例如微粒体Ca(2+)-ATP酶抑制剂毒胡萝卜素。现在可以通过膜片钳记录、钙依赖性染料、报告基因和荧光视频技术在单细胞水平上研究离子通道、膜电位、[Ca2+]i和淋巴因子基因表达之间复杂的因果关系。这些方法将有助于阐明离子通道在支持活化和其他淋巴细胞行为的分子途径中的重要作用。
