Spontaneous transient outward currents arise from microdomains where BK channels are exposed to a mean Ca(2+) concentration on the order of 10 microM during a Ca(2+) spark.
Spontaneous transient outward currents arise from microdomains where BK channels are exposed to a mean Ca(2+) concentration on the order of 10 microM during a Ca(2+) spark.
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DOI：
10.1085/jgp.20028571
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发表时间：
2002-07
影响因子：
3.8
通讯作者：
Walsh, John V Jr
中科院分区：
文献类型：
--
作者：
Zhuge, Ronghua;Fogarty, Kevin E;Tuft, Richard A;Walsh, John V Jr
Ca2+ 火花是由于 Ca2+ 通过兰尼碱受体从肌浆网释放而引起的小型局部胞质 Ca2+ 瞬变。在平滑肌中，Ca2+火花激活火花微区中大电导Ca2+激活的K+通道（BK通道），从而产生自发瞬态外向电流（STOC）。本研究的目的是通过实验确定 BK 通道在火花期间暴露的 Ca2+ 水平。使用紧密密封的全细胞记录，我们分析了 STOC 电导 (g(STOC)) 的电压依赖性，并将其与存在不同 [Ca2+] 的情况下切除的斑块中 BK 通道激活的电压依赖性进行比较。 Ca2+ 火花的振幅在感兴趣的电位范围内没有变化。相比之下，g(STOC) 的幅度在 20 至 -40 mV 范围内大致保持恒定，然后在更负的电位下急剧下降。根据这一点以及 BK 通道激活的电压依赖性，我们得出结论，STOC 下的 BK 通道在 Ca2+ 火花期间暴露于约 10 μM 的平均 [Ca2+]。达到浓度≥10 μM 的膜区域的估计半径为 150–300 nm，对应于一平方微米的一小部分区域。此外，考虑到估计的通道密度和火花期间的 Ca2+ 电流所施加的限制，BK 通道似乎并不是均匀分布在膜上，而是在火花部位以更高的密度被发现。
Ca2+ sparks are small, localized cytosolic Ca2+ transients due to Ca2+ release from sarcoplasmic reticulum through ryanodine receptors. In smooth muscle, Ca2+ sparks activate large conductance Ca2+-activated K+ channels (BK channels) in the spark microdomain, thus generating spontaneous transient outward currents (STOCs). The purpose of the present study is to determine experimentally the level of Ca2+ to which the BK channels are exposed during a spark. Using tight seal, whole-cell recording, we have analyzed the voltage-dependence of the STOC conductance (g(STOC)), and compared it to the voltage-dependence of BK channel activation in excised patches in the presence of different [Ca2+]s. The Ca2+ sparks did not change in amplitude over the range of potentials of interest. In contrast, the magnitude of g(STOC) remained roughly constant from 20 to −40 mV and then declined steeply at more negative potentials. From this and the voltage dependence of BK channel activation, we conclude that the BK channels underlying STOCs are exposed to a mean [Ca2+] on the order of 10 μM during a Ca2+ spark. The membrane area over which a concentration ≥10 μM is reached has an estimated radius of 150–300 nm, corresponding to an area which is a fraction of one square micron. Moreover, given the constraints imposed by the estimated channel density and the Ca2+ current during a spark, the BK channels do not appear to be uniformly distributed over the membrane but instead are found at higher density at the spark site.