CA-2+ INDUCES CHARYBDOTOXIN-SENSITIVE MEMBRANE-POTENTIAL CHANGES IN RAT LYMPHOCYTES
CA-2+ INDUCES CHARYBDOTOXIN-SENSITIVE MEMBRANE-POTENTIAL CHANGES IN RAT LYMPHOCYTES
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DOI：
10.1152/ajpcell.1989.257.2.c197
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发表时间：
1989-08-01
影响因子：
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通讯作者：
SMITH, JD
中科院分区：
文献类型：
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作者：
GRINSTEIN, S;SMITH, JD
关于淋巴细胞中Ca2+激活的K+通道的存在存在分歧。据报道，随着游离胞质Ca2+浓度（[Ca2+]i）的升高，膜电位（Em）发生去极化、超极化或微小变化。贴片夹紧研究已经证明抑制电压门控K+通道，但Ca2+激活的K+通道尚未被检测到。我们使用charybdotoxin (CTX)，一种Ca2+激活的K+通道的有效抑制剂，来评估它们在大鼠胸腺淋巴细胞中的存在。用荧光探针测定离子霉素处理后细胞悬液中的Em和[Ca2+]i。在基础[Ca2+]i， CTX对Em没有影响，这表明Ca2+激活的K+通道对静息电位没有重要贡献。[Ca2+]i在亚微摩尔范围内的升高诱导了依赖于向外K+梯度的超极化。Em变化的形状和持续时间与[Ca2+]i的升高密切相关。这种超极化被纳摩尔浓度的CTX抑制。当[Ca2+]i接近或超过1 μ时。M，一个双相的Em chan，被记录下来。短暂的、ctx敏感的超极化之后是持续的去极化。当忽略外部Na+时，后者大大降低。这些数据表明胸腺淋巴细胞具有Ca2+敏感的K+通道，这些通道被[Ca2+]i的适度增加激活，导致超极化。在较高的[Ca2+]i下，K+通道对Em的影响被非选择性阳离子通道的打开所取代，产生去极化。在早期的研究中获得的[Ca2+]i水平的变化可以解释现有的差异。
There is disagreement regarding the existence of Ca2+-activated K+ channels in lymphocytes. Depolarization, hyperpolarization, or little change in membrane potential (Em) has been reported following elevation of free cytosolic Ca2+ concentration ([Ca2+]i). Patch-clamping studies have demonstrated inhibition of voltage-gated K+ channels, but Ca2+-activated K+ channels have not been detected. We used charybdotoxin (CTX), a potent inhibitor of Ca2+-activated K+ channels, to assess their presence in rat thymic lymphocytes. Fluorescent probes were used to measure Em and [Ca2+]i in cell suspensions treated with ionomycin. At basal [Ca2+]i, CTX had no effect on Em, suggesting that Ca2+-activated K+ channels do not contribute importantly to the resting potential. Elevation of [Ca2+]i in the submicromolar range induced a hyperpolarization that was dependent on the outward K+ gradient. the shape and duration of the Em change closely followed the elevation of [Ca2+]i. This hyperpolarization was inhibited by nanomolar concentrations of CTX. When [Ca2+]i approached or exceeded 1 .mu.M, a biphasic Em chan, was recorded. A transient, CTX-sensitive hyperpolarization was followed by a sustained depolarization. The latter was greatly reduced when external Na+ was omitted. The data suggest that thymic lymphocytes possess Ca2+-sensitive K+ channels, which are activated by moderate increases in [Ca2+]i, resulting in hyperpolarization. At higher [Ca2+]i the effect of K+ channels on Em is superseded by opening of nonselective cation channels, producing depolarization. Variations in the level of [Ca2+]i attained in earlier studies can explain existing discrepancies.