Ion selectivities of the Ca2+ sensors for exocytosis in rat phaeochromocytoma cells
Ion selectivities of the Ca2+ sensors for exocytosis in rat phaeochromocytoma cells
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DOI：
10.1111/j.1469-7793.2001.t01-1-00627.x
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发表时间：
2001-06
期刊：
影响因子：
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通讯作者：
T. Kishimoto;Ting‐ting Liu;Y. Ninomiya;Hiroshi Takagi;T. Yoshioka;G. Ellis‐Davies;Yasushi Miyashita;H. Kasai
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文献类型：
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作者：
T. Kishimoto;Ting‐ting Liu;Y. Ninomiya;Hiroshi Takagi;T. Yoshioka;G. Ellis‐Davies;Yasushi Miyashita;H. Kasai
用膜电容法和电流法测定了大鼠嗜铬细胞瘤（PC12）细胞中Ca2+传感器对胞外分泌两组分的离子选择性。通过光解笼状Ca2+化合物增加细胞内金属离子浓度，并用低亲和力指示剂苯并噻唑香豆素（BTC）或5 -硝基苯并噻唑香豆素（BTC - 5N）测定。2 Ca2+诱导的膜电容增加分为两个阶段，时间常数为30 ~ 100 ms和5 s。反映大致密核囊泡胞吐的电流事件选择性地发生在慢期，即使胞质Ca2+浓度增加0.1 mM。3胞吐的慢组分被所有被研究的金属离子激活，包括Cd2+（中位有效浓度，18 pM）、Mn2+ (500 nM)、Co2+ (900 nM)、Ca2+ (8 μM)、Sr2+ (180 μM)、Ba2+ (280 μM)和Mg2+ (> 5 mM)。相比之下，Cd2+ (26 pM)、Mn2+ (620 nM)、Ca2+ (24 μM)和Sr2+ (320 μM)激活了胞吐的快速组分，但Ba2+ (bbb2.0 mM)和Co2+仅略微增加，Mg2+则没有增加。快速组分被Na+（有效浓度中位数为44 mM）竞争性阻断，而不被Li+、K+或Cs+竞争性阻断。因此，对胞吐快速组分的Ca2+传感器比对慢速组分的Ca2+传感器更具选择性；此外，这种选择性似乎是基于离子半径，阳离子半径为0.84至1.13 Å （1 Å= 0.1 nm）是有效的。这些数据支持synaptotagmin -磷脂作为Ca2+传感器在大的致密核囊泡胞外分泌中的作用，并表明在突触样囊泡的同步胞外分泌中还有一种额外的Ca2+感应机制。
1 The ion selectivities of the Ca2+ sensors for the two components of exocytosis in rat phaeochromocytoma (PC12) cells were examined by measurement of membrane capacitance and amperometry. The cytosolic concentrations of metal ions were increased by photolysis of caged‐Ca2+ compounds and measured with low‐affinity indicators benzothiazole coumarin (BTC) or 5‐nitrobenzothiazole coumarin (BTC‐5N). 2 The Ca2+‐induced increases in membrane capacitance comprised two phases with time constants of 30‐100 ms and 5 s. Amperometric events reflecting the exocytosis of large dense‐core vesicles occurred selectively in the slow phase, even with increases in the cytosolic Ca2+ concentration of > 0.1 mM. 3 The slow component of exocytosis was activated by all metal ions investigated, including Cd2+ (median effective concentration, 18 pM), Mn2+ (500 nM), Co2+ (900 nM), Ca2+ (8 μM), Sr2+ (180 μM), Ba2+ (280 μM) and Mg2+ (> 5 mM). In contrast, the fast component of exocytosis was activated by Cd2+ (26 pM), Mn2+ (620 nM), Ca2+ (24 μM) and Sr2+ (320 μM), but was only slightly increased by Ba2+ (> 2 mM) and Co2+ and not at all by Mg2+. 4 The fast component, but not the slow component, was competitively blocked by Na+ (median effective concentration, 44 mM) but not by Li+, K+ or Cs+. Thus, the Ca2+ sensor for the fast component of exocytosis is more selective than is that for the slow component; moreover, this selectivity appears to be based on ionic radius, with cations with radii of 0.84 to 1.13 Å (1 Å= 0.1 nm) being effective. 5 These data support a role for synaptotagmin‐phospholipid as the Ca2+ sensor for the exocytosis of large dense‐core vesicles and they suggest that an additional Ca2+‐sensing mechanism operates in the synchronous exocytosis of synaptic‐like vesicles.