Yoshino M, Matsufuji Y, Yabu H
Department of Physiology, Sapporo Medical University, Japan.
Can J Physiol Pharmacol. 1995 Jan;73(1):27-35. doi: 10.1139/y95-004.
The properties of Ca(2+)-mediated inactivation as revealed by a conventional double-pulse protocol were examined by using the whole-cell patch clamp technique. A U-shaped relationship between the conditioning potential and the Ca2+ current (ICa) inactivation was observed, with a maximum inactivation of 52 +/- 4% (n = 5) at 10 mV with 0.5 mM EGTA in the patch pipettes. The maximum inactivation was reduced significantly, to 31 +/- 5.7% (n = 12) and 32 +/- 7.0% (n = 5), when a high concentration of EGTA (20 mM) or a more efficient Ca2+ chelator, BAPTA, was included in the patch pipettes, respectively. The same double-pulse protocol was applied under conditions where the stored Ca2+ was depleted by using caffeine or the stored Ca2+ release function was blocked by using ryanodine or procaine and heparin. No significant difference in the maximum ICa inactivation before (45%) and after (50%) application of 10 mM caffeine was observed. The maximum ICa inactivations of 48 +/- 3.2% (n = 4) and 52 +/- 8.4% (n = 6) were still observed after treatment of the cell with ryanodine (20 microM) or loading 10 mM procaine and 1 mg/mL heparin in the patch pipettes, respectively. These results suggest that Ca2+ mobilization from an internal Ca2+ store is not essential for the Ca(2+)-mediated inactivation observed in the double-pulse experiment, rather influx of Ca2+ through a voltage-dependent Ca channel seems to be important for ICa inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)
采用全细胞膜片钳技术，通过传统双脉冲方案研究了Ca(2+)介导的失活特性。观察到预处理电位与Ca2+电流（ICa）失活之间呈U形关系，在膜片电极中含有0.5 mM EGTA时，在10 mV下最大失活率为52±4%（n = 5）。当膜片电极中分别含有高浓度EGTA（20 mM）或更有效的Ca2+螯合剂BAPTA时，最大失活率显著降低，分别为31±5.7%（n = 12）和32±7.0%（n = 5）。在使用咖啡因耗尽储存的Ca2+或使用ryanodine或普鲁卡因和肝素阻断储存的Ca2+释放功能的条件下，应用相同的双脉冲方案。在施加10 mM咖啡因之前（45%）和之后（50%），未观察到最大ICa失活有显著差异。在用ryanodine（20 μM）处理细胞或在膜片电极中加载10 mM普鲁卡因和1 mg/mL肝素后，仍分别观察到最大ICa失活率为48±3.2%（n = 4）和52±8.4%（n = 6）。这些结果表明，从内部Ca2+储存库中动员Ca2+对于双脉冲实验中观察到的Ca(2+)介导的失活不是必需的，相反，通过电压依赖性Ca通道的Ca2+内流似乎对ICa失活很重要。（摘要截短于250字）
