Fierro L, Parekh A B
Laboratory of Molecular and Cellular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
J Membr Biol. 1999 Mar 1;168(1):9-17. doi: 10.1007/s002329900493.
Fast inactivation of the Ca2+ release-activated Ca2+ current (ICRAC) was studied using whole cell patch-clamp recordings in rat basophilic leukemia (RBL-1) cells. Application of hyperpolarizing voltage steps from the holding potential of 0 mV revealed that ICRAC declined in amplitude over tens of milliseconds during steps more negative than -40 mV. This fast inactivation was predominantly Ca2+-dependent because first, it could be more effectively suppressed when BAPTA was included in the recording pipette instead of EGTA and second, replacing external Ca2+ with Sr2+ resulted in less inactivation. Recovery from inactivation was faster in the presence of BAPTA than EGTA. The extent of fast inactivation was independent of the whole cell ICRAC amplitude, compatible with the notion that the inactivation arose from a local feedback inhibition by permeating Ca2+ ions only on the channel it permeated. Ca2+ release from stores did not affect fast inactivation, nor did FCepsilonRI receptor stimulation. Current clamp recordings showed that the majority of RBL cells had a membrane potential close to -90 mV following stimulation of FCepsilonRI receptors. Hence fast inactivation is likely to impact on the extent of Ca2+ influx through CRAC channels under physiological conditions and appears to be an important negative feedback process that limits Ca2+ increases.
利用全细胞膜片钳记录技术，在大鼠嗜碱性白血病（RBL-1）细胞中研究了钙释放激活钙电流（ICRAC）的快速失活。从0 mV的钳制电位施加超极化电压阶跃，结果显示，在比-40 mV更负的电压阶跃期间，ICRAC的幅度在数十毫秒内下降。这种快速失活主要依赖于Ca2+，原因如下：其一，当记录电极内液中加入BAPTA而非EGTA时，快速失活能得到更有效的抑制；其二，用Sr2+替代细胞外Ca2+会导致失活程度降低。在存在BAPTA的情况下，失活恢复比存在EGTA时更快。快速失活的程度与全细胞ICRAC幅度无关，这与失活源于仅由通过通道的Ca2+离子对其自身进行局部反馈抑制的观点相符。从储存库释放Ca2+并不影响快速失活，FcεRI受体刺激也不影响。电流钳记录显示，在刺激FcεRI受体后，大多数RBL细胞的膜电位接近-90 mV。因此，在生理条件下，快速失活可能会影响通过CRAC通道的Ca2+内流程度，并且似乎是一个限制Ca2+增加的重要负反馈过程。
