TRANSIENT INWARD CURRENT IN GUINEA-PIG ATRIAL MYOCYTES REFLECTS A CHANGE OF SODIUM-CALCIUM EXCHANGE CURRENT
TRANSIENT INWARD CURRENT IN GUINEA-PIG ATRIAL MYOCYTES REFLECTS A CHANGE OF SODIUM-CALCIUM EXCHANGE CURRENT
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DOI：
10.1113/jphysiol.1988.sp017021
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发表时间：
1988-03-01
影响因子：
5.5
通讯作者：
POTT, L
中科院分区：
文献类型：
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作者：
LIPP, P;POTT, L
1.用全细胞膜片钳技术对成年豚鼠心肌细胞进行电压钳制。用于内部透析的移液管填充溶液含有65 mM-柠檬酸盐和50 μ M-EGTA作为Ca 2+螯合剂和20 mM-Na+。通过用CS+替换膜两侧的该离子来阻断钾通道电流。2.在上述条件下，肌细胞在恒定的负膜保持电位下产生自发的瞬时内向电流（Iti）。在给定的膜电位下，可以以恒定的振幅和频率记录Iti，时间长达ca。通过用含咖啡因（5-10 mM）的溶液灌注细胞，可以诱发具有类似性质的膜电流。3.去极化导致Iti振幅降低并延长其持续时间。在膜电位阶跃变化至约100 mV后，-10 mV或负性较小的水平，仅观察到一个内向电流变化。此后，膜电流相对于该膜电位下的瞬时电流保持向内。完全放松的Iti，然后才能观察到复极后，更负的膜电位。4.肌浆Ca ~（2+）释放引起的电流变化在-90 ~+75mV的膜电位范围内是向内的。Iti的逆转从未被检测到。5.瞬时电流-电压（I-V）关系和峰值Iti的电压依赖性显示出明显的外向整流。这两个I-V关系可以描述由生电Na+-Ca 2+交换（INa，Ca）假设3：1的化学计量和膜的电场中的单个能垒引起的膜电流的形式主义。6. Iti的时间积分在保持电位的增加后，观察到去极化到正膜电位，其中外向整流电流分量是突出的。这支持了这样的观点，即外向电流代表“反向模式”的INa，Ca，携带Ca 2+离子进入细胞。7.在长时间的细胞透析后，观察到Iti的下降。由于在这种情况下，强去极化仍然可以在复极化时引起内向电流，所以下降可能反映了肌浆网功能的受损，而不是细胞透析对交换器的影响。8.我们的结论是，在目前的条件下，膜电流的测量，这在很大程度上决定了“被动”的I-V曲线的肌细胞。该电流通过肌浆Ca 2+释放后Ca 2+升高而改变。该电流的性质、其电压依赖性以及细胞内Ca 2+瞬态对电压依赖性的影响与生电Na+-CA 2+交换作为电荷携带机制高度兼容。
1. Enzymatically isolated, cultured myocytes from hearts of adult guinea-pigs were voltage clamped with a whole-cell patch-clamp technique. The pipette-filling solution for internal dialysis contained 65 mM-citrate and 50 .mu.M-EGTA as Ca2+-chelating agents and 20 mM-Na+. Potassium channel currents were blocked by replacing this ion on both sides of the membrane by CS+. 2. In the above conditions myocytes develop spontaneous transient inward currents (Iti) at constant negative membrane holding potentials. At a given membrane potential Iti can be recorded with constant amplitude and frequency for periods up to ca. 40 min. A membrane current with similar properties can be evoked by superfusion of the cell with caffeine-containing (5-10 mM) solution. 3. Depolarization results in a reduction of Iti amplitude and a prolongation of its duration. After a step change of the membrane potential to ca. -10 mV or a less-negative level only one inward current change is observed. Thereafter the membrane current remains inward with regard to the instantaneous current at this membrane potential. Complete relaxation of Iti then is only observed after repolarization to a more-negative membrane potential. 4. The currrent changes caused by sarcoplasmic Ca2+ release is inward in a range of membrane potentials between -90 and +75 mV. A reversal of Iti was never detected. 5. Both the instantaneous current-voltage (I-V) relation and voltage dependence of peak Iti display distinct outward rectification. Both I-V relations can be described by a formalism suggested for a membrane current caused by electrogenic Na+-Ca2+ exchange (INa, Ca) assuming a 3:1 stoichiometry and a single energy barrier in the electrical field of the membranes. 6. An increase of the time integral of Iti at the holding potential is observed after depolarizations to positive membrane potentials, where the outward-rectifying current component is prominent. This supports the view that the outward current represents INa,Ca in the ''reverse mode'', carrying Ca2+ ions into the cell. 7. After prolonged cell dialysis a run-down of Iti is observed. Since strong depolarizations in this condition still can caused inward currents upon repolarization, run-down is likely to reflect an impairment of sarcoplasmic reticulum function rather than an effect of cell dialysis on the exchanger. 8. We conclude that under the present conditions a membrane current is measured, which to a large extent determines the ''passive'' I-V curve of the myocytes. This current is modified by a rise in Cai2+ following sarcoplasmic Ca2+ release. The properties of this current, its voltage dependence, and the effect of an intracellular Ca2+ transient on the voltage dependence, are highly compatible with electrogenic Na+-CA2+ exchange as a charge-carrying mechanism.