Lawrence C, Rodrigo G C
Department of Physiology, School of Medical Sciences, University of Otago, Dunedin, New Zealand.
Pflugers Arch. 1999 May;437(6):831-8. doi: 10.1007/s004240050852.
The effects of removing extracellular Ca2+ and Mg2+ on the membrane potential, membrane current and intracellular Na+ activity (aiNa) were investigated in guinea-pig and rat ventricular myocytes. Membrane potential was recorded with a patch pipette and whole-cell membrane currents using a single-electrode voltage clamp. Both guinea-pig and rat cells depolarize when the bathing Ca2+ and Mg2+ are removed and the steady-state aiNa increases rapidly from a resting value of 6.4+/- 0.6 mM to 33+/-3.8 mM in guinea-pig (n=9) and from 8.9+/-0.8 mM to 29.3+/-3.0 mM (n=5) in rat ventricular myocytes. Guinea-pig myocytes partially repolarized when, in addition to removal of the bathing Ca2+ and Mg2+, K+ was also removed, however rat cells remained depolarized. A large diltiazem-sensitive inward current was recorded in guinea-pig and rat myocytes, voltage-clamped at -20 mV, when the bathing divalent cations were removed. When the bathing K+ was removed after Ca2+ and Mg2+ depletion, a large outward K+ current developed in guinea-pig, but not in rat myocytes. This current had a reversal potential of -80+/-0.7 mV and was not inhibited by high Mg2+ or glybenclamide indicating that it is not due to activation of non-selective cation or adenosine triphosphate (ATP)-sensitive K channels. The current was not activated when Li+ replaced the bathing Na+ and was blocked by R-56865, suggesting that it was due to the activation of KNa channels.
在豚鼠和大鼠心室肌细胞中研究了去除细胞外Ca²⁺和Mg²⁺对膜电位、膜电流和细胞内Na⁺活性(aiNa)的影响。用膜片吸管记录膜电位,使用单电极电压钳记录全细胞膜电流。当去除灌流液中的Ca²⁺和Mg²⁺时,豚鼠和大鼠细胞均发生去极化,并且稳态aiNa迅速从豚鼠静息值6.4±0.6 mM增加到33±3.8 mM(n = 9),在大鼠心室肌细胞中从8.9±0.8 mM增加到29.3±3.0 mM(n = 5)。当除了去除灌流液中的Ca²⁺和Mg²⁺之外还去除K⁺时,豚鼠心肌细胞部分复极化,然而大鼠细胞仍保持去极化状态。当去除灌流的二价阳离子时,在钳制电压为-20 mV的豚鼠和大鼠心肌细胞中记录到一个大的地尔硫䓬敏感内向电流。当在Ca²⁺和Mg²⁺耗竭后去除灌流的K⁺时,豚鼠心肌细胞中出现一个大的外向K⁺电流,但大鼠心肌细胞中未出现。该电流的反转电位为-80±0.7 mV,并且不受高Mg²⁺或格列本脲抑制,表明它不是由于非选择性阳离子或三磷酸腺苷(ATP)敏感性K⁺通道的激活所致。当Li⁺替代灌流的Na⁺时该电流未被激活,并且被R - 56865阻断,提示它是由于KNa通道的激活所致。