Rapid charge translocation by the cardiac Na+-Ca2+ exchanger after a Ca2+ concentration jump
Rapid charge translocation by the cardiac Na+-Ca2+ exchanger after a Ca2+ concentration jump
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DOI：
10.1016/s0006-3495(96)79441-9
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发表时间：
1996-11-01
影响因子：
3.4
通讯作者：
Hartung, K
中科院分区：
文献类型：
--
作者：
Kappl, M;Hartung, K
在离体豚鼠或大鼠心脏巨膜膜片上测定了胞浆Ca ~（2+）浓度跃变（通过DM-nitrophen光解实现）后Na ~+-Ca ~（2+）交换电流的动力学。在100 mM细胞外Na+存在下，将细胞质Ca 2+浓度从0.5 μ M增加到100 μ M，产生内向电流，在21 ℃下，该内向电流以时间常数τ（1）< 50 μ s上升，并以时间常数τ（2）= 0.65 +/-0.18 ms（n = 101）衰减到平台，这些电流信号被Ni ~（2+）和二氯苯脒抑制。如果在促进Ca 2 +-Ca 2+交换的条件下（即，无细胞外Na+，5 mM细胞外Ca ~（2+）），在细胞外Ca ~（2+）和Na+不存在时，未观察到瞬时和稳态内向电流。α-糜蛋白酶的应用揭示了细胞质调节Ca 2+结合位点对Ca 2 +-Ca 2+和正向Na+-Ca 2+交换的影响，并表明该位点调节瞬时和稳态电流。稳态电流的温度依赖性表现出在21 ° C和38 ° C之间的温度为70 kJ/mol的活化能，在10 ° C和21 ° C之间为138 kJ/mol。对于衰减时间常数，在Na+-Ca 2+和Ca 2 +-Ca 2+交换模式中在13 ° C和35 ° C之间观察到70 kJ/mol的活化能。数据表明，与Ca 2+结合和易位相关的Na+-Ca 2+交换剂的部分反应在35 ° C下非常快，在正向Na+-Ca 2+交换模式中具有约6700 s（-1）的弛豫时间常数，在Ca 2 +-Ca 2+交换模式中具有约12，500 s（-1）的弛豫时间常数，并且在Ca 2+易位期间净负电荷移动。然而，根据模型计算，必须比瞬时电流的衰减速率小至少2-4倍，并且Na+向内移位似乎比Ca 2+向外移动慢。
The kinetics of Na+-Ca2+ exchange current after a cytoplasmic Ca2+ concentration jump (achieved by photolysis of DM-nitrophen) was measured in excised giant membrane patches from guinea pig or rat heart. Increasing the cytoplasmic Ca2+ concentration from 0.5 mu M to 100 mu M in the presence of 100 mM extracellular Na+ elicits an inward current that rises with a time constant tau(1) < 50 mu s and decays to a plateau with a time constant tau(2) = 0.65 +/- 0.18 ms (n = 101) at 21 degrees C, These current signals are suppressed by Ni2+ and dichlorobenzamil. No stationary current, but a transient inward current that rises with tau(1) < 50 mu s and decays with tau(2) = 0.28 +/- 0.06 ms (n = 53, T = 21 degrees C) is observed if the Ca2+ concentration jump is performed under conditions that promote Ca2+-Ca2+ exchange (i.e., no extracellular Na+, 5 mM extracellular Ca2+), The transient and stationary inward current is not observed in the absence of extracellular Ca2+ and Na+. The application of alpha-chymotrypsin reveals the influence of the cytoplasmic regulatory Ca2+ binding site on Ca2+-Ca2+ and forward Na+-Ca2+ exchange and shows that this site regulates both the transient and stationary current. The temperature dependence of the stationary current exhibits an activation energy of 70 kJ/mol for temperatures between 21 degrees C and 38 degrees C, and 138 kJ/mol between 10 degrees C and 21 degrees C. For the decay time constant an activation energy of 70 kJ/mol is observed in the Na+-Ca2+ and the Ca2+-Ca2+ exchange mode between 13 degrees C and 35 degrees C, The data indicate that partial reactions of the Na+-Ca2+ exchanger associated with Ca2+ binding and translocation are very fast at 35 degrees C, with relaxation time constants of about 6700 s(-1) in the forward Na+-Ca2+ exchange and about 12,500 s(-1) in the Ca2+-Ca2+ exchange mode and that net negative charge is moved during Ca2+ translocation, According to model calculations, the turnover number, however, has to be at least 2-4 times smaller than the decay rate of the transient current, and Na+ inward translocation appears to be slower than Ca2+ outward movement.