Intracellular calcium and Na+-Ca2+ exchange current in isolated toad pacemaker cells
Intracellular calcium and Na+-Ca2+ exchange current in isolated toad pacemaker cells
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DOI：
10.1111/j.1469-7793.1998.153br.x
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发表时间：
1998-04-01
影响因子：
5.5
通讯作者：
Allen, DG
中科院分区：
文献类型：
--
作者：
Ju, YK;Allen, DG
1. 从蟾蜍静脉窦中分离单个起搏器细胞，研究动作电位自发放电速率的机制。用吲哚-1测定细胞内钙浓度（[Ca2+](i)），以确定[Ca2+](i)是否影响放电速率。[Ca2+](i)的瞬时快速升高与自发动作电位一起被记录下来。[Ca2+](i)收缩期峰值655 +/- 64 nM，舒张末期最低195 +/- 15 nM.2。细胞外Ca2+浓度从2降低到0.5 mM引起收缩和舒张[Ca2+]的降低(i)，自发放电率也逐渐下降。应用BAPTA的乙酰氧基甲基（AM）酯（10 μ M），以增加细胞内钙缓冲，引起收缩压和舒张压[Ca2+]下降(i)。放电速率逐渐下降，直至10-15 min后细胞停止放电。在放电停止时，舒张[Ca2+](i)下降了141 +/- 38 nM.4。在ryanodine （2 μ M）的存在下，它干扰Ca2+从肌浆网释放，收缩和舒张[Ca2+](i)都下降，放电率下降，直到细胞停止放电。静息时舒张[Ca2+](i)下降93 +/- 20 nm。细胞暴露于无Na+溶液导致[Ca2+](i)升高，在4.8 +/- 0.3 s后超过收缩期水平。这种上升与Ca2+进入Na+-Ca2+交换器是一致的。将咖啡因（10-20 mM）快速应用于夹夹在-60 mV的细胞，导致[Ca2+](i)迅速增加，然后自发下降。同时也产生了与[Ca2+](i)时间过程相似的向内电流。Ni2+ (5 mM)或2,4-二氯苯苄胺（25 μ M）分别使咖啡因产生的向内电流振幅降低了96 +/- 1%和74 +/- 10%。在无Na+溶液中，咖啡因诱导电流降低了93 +/- 7%。在各种情况下，舒张[Ca2+](i)显示与起搏器放电率密切相关。Na+-Ca2+交换器的存在及其对起搏器电位期间内向电流的估计贡献表明，Na+-Ca2+交换电流对起搏器活性有贡献。
1. Single pacemaker cells were isolated from the sinus venosus of cane toad (Bufo marinus) in order to study the mechanisms involved in the spontaneous firing rate of action potentials. Intracellular calcium concentration ([Ca2+](i)) was measured with indo-1 to determine whether [Ca2+](i) influenced firing rate. A rapid transient rise of [Ca2+](i) was recorded together with each spontaneous action potential. [Ca2+](i) at the peak of systole was 655 +/- 64 nM and the minimum at the end of diastole was 195 +/- 15 nM.2. Reduction of extracellular Ca2+ concentration from 2 to 0.5 mM caused a reduction in both systolic and diastolic [Ca2+](i) and the spontaneous firing rate also gradually declined.3. Application of the acetoxymethyl (AM) ester of BAPTA (10 mu M), in order to increase intracellular calcium buffering, caused a decline in systolic and diastolic [Ca2+](i). The firing rate declined progressively until the cells stopped firing after 10-15 min. At the time that firing ceased, the diastolic [Ca2+](i) had declined by 141 +/- 38 nM.4. In the presence of ryanodine (2 mu M), which interferes with Ca2+ release from the sarcoplasmic reticulum, the systolic and diastolic [Ca2+](i) both declined and the firing rate decreased until the cells stopped firing. At quiescence diastolic [Ca2+](i) had declined by 93 +/- 20 nM.5. Exposure of the cells to Na+-free solution caused a rise in [Ca2+](i) which exceeded the systolic level after 4.8 +/- 0.3 s. This rise is consistent with Ca2+ entry on a Na+-Ca2+ exchanger.6. Rapid application of caffeine (10-20 mM) to cells clamped at -60 mV caused a rapid increase in [Ca2+](i) which then spontaneously declined. An inward current with a similar time course to that of [Ca2+](i) was also generated. Application of Ni2+ (5 mM) or 2,4-dichlorobenzamil (25 mu M) reduced the amplitude of the inward current produced by caffeine by 96 +/- 1 % and 74 +/- 10%, respectively. In a Na+-free solution the caffeine-induced current was reduced by 93 +/- 7%.7. Under a variety of circumstances the diastolic [Ca2+](i) showed a close association viith pacemaker firing rate. The existence of a Na+-Ca2+ exchanger and its estimated contribution to inward current during the pacemaker potential suggest that the Na+-Ca2+ exchange current makes a contribution to pacemaker activity.