Tsuchida K, Otomo S
Research Center, Taisho Pharmaceutical Co., Ltd., Saitama, Japan.
Eur J Pharmacol. 1990 Nov 13;190(3):313-20. doi: 10.1016/0014-2999(90)94195-4.
Monensin, a monovalent cation ionophore, transports sodium ions preferentially. We found that, in the cardiac Purkinje fibers, monensin 10(-5) M increased the resting tension of the fiber bundle in Tyrode solution containing 4.5 mM Ca. This ionophore (10(-5) M) shortened the duration of the action potential and suppressed the pacemaker potential. In Na-free or Ca-free solutions, monensin had no effect on the configuration of the action potential. In voltage clamp experiments, monensin 10(-5) M shifted the holding current at -40 mV outwardly, increased the instantaneous inward current (possibly inward rectifying potassium current, IK1) and increased the transient outward current (Ito), whereas it attenuated the hyperpolarization-activated inward current (If). The delayed rectifying outward current (IK) was not significantly affected by monensin 10(-5) M. The transient inward current (ITI) appeared in the presence of monensin 10(-5) M. These changes induced by monensin are consistent with changes in configuration of the action potential induced by monensin. The membrane current changes are considered to be induced by an increase in intracellular Ca concentration, probably via a Na-Ca exchange following an increase in intracellular Na concentration, and by alteration of intra- and extracellular Na and K concentrations.
莫能菌素是一种单价阳离子离子载体，优先转运钠离子。我们发现，在心脏浦肯野纤维中，10⁻⁵ M的莫能菌素可增加含4.5 mM钙的台氏液中纤维束的静息张力。这种离子载体（10⁻⁵ M）缩短了动作电位的持续时间并抑制了起搏电位。在无钠或无钙溶液中，莫能菌素对动作电位的形态没有影响。在电压钳实验中，10⁻⁵ M的莫能菌素使-40 mV时的钳制电流向外移动，增加了瞬时内向电流（可能是内向整流钾电流，IK1）并增加了瞬时外向电流（Ito），而减弱了超极化激活的内向电流（If）。10⁻⁵ M的莫能菌素对延迟整流外向电流（IK）没有显著影响。在10⁻⁵ M的莫能菌素存在下出现了瞬时内向电流（ITI）。莫能菌素引起的这些变化与莫能菌素诱导的动作电位形态变化一致。膜电流变化被认为是由细胞内钙浓度升高引起的，可能是通过细胞内钠浓度升高后的钠-钙交换，以及细胞内和细胞外钠和钾浓度的改变引起的。
