Han X, Ferrier G R
Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.
J Mol Cell Cardiol. 1996 Oct;28(10):2069-84. doi: 10.1006/jmcc.1996.0200.
Two-microelectrode voltage-clamp technique was applied and a number of experimental manoeuvres were used to determine the charge-carrying systems of the arrhythmogenic transient inward current (TI) in rabbit cardiac Purkinje fibres. Increasing [Ca2+]o to 30 mmol/l (in the presence of [Na+]o) induced TI with a clear-cut reversal potential around -23 mV. This observation suggests that the TI is conducted through an ionic channel. Nickel chloride (2.5 mmol/l) which blocks Na+/Ca2+ exchange current greatly decreased peak inward TI (57 +/- 3%) but significantly increased peak outward TI (86.4 +/- 9.6%), which suggests that Na+ Ca2+ exchange is not the charge-carrying system for TI. In experiments in which TI was induced when [Na+]o was replaced by either N-methyl-D-glucamine, choline, or sucrose (to eliminate Na+ Ca2+ exchange), Ni2+ still decreased inward TI and increased outward TI. There was no significant difference between the effects of Ni2+ in the presence and absence of [Na+]o. The effects of Ni2+ in the absence of [Na+]o confirm that Ni(2+)-induced attenuation of inward TI is not mediated by the Na+ Ca2+ exchange, but rather through an inhibition of TI channels. Acute exposure to Mn2+ (5 mmol/l) almost abolished inward TI at a time when outward TI just showed a slight decrease. A third divalent cation, Cd2+ (0.25-1.0 mmol/l), strongly suppressed both inward and outward TI at the same time. The opposite effects of Ni2+ on inward v outward TI and the preferential inhibition of inward TI by Mn2- suggest involvement of multiple ionic channels in conducting TI. 4.4'-diisothiocyanatostilbene-2.2' disulfonic acid (DIDS, 10 mumol/l) and 4-acetamido-4'-isothicyanatostilbene-2.2' disulfonic acid (SITS. 0.2 mmol/l), which block CI- conductance in cardiac tissues, dramatically suppressed outward TI (80 +/- 9%) but to a lesser extent inward TI (20 +/- 4%). Our results suggest that, in cardiac Purkinje fibres, high [Ca2+]o induced TI is conducted mainly through TI channels which fall into two different populations: cationic and anionic.
采用双微电极电压钳技术，并运用多种实验操作来确定兔心脏浦肯野纤维中致心律失常性瞬时内向电流（TI）的载流系统。将细胞外钙离子浓度（[Ca2+]o）提高到30 mmol/L（细胞外钠离子浓度[Na+]o存在时）可诱发TI，其反转电位约为 -23 mV，十分明确。这一观察结果表明，TI是通过离子通道传导的。氯化镍（2.5 mmol/L）可阻断钠钙交换电流，使内向TI峰值大幅降低（57±3%），但外向TI峰值显著增加（86.4±9.6%），这表明钠钙交换不是TI的载流系统。在用N-甲基-D-葡萄糖胺、胆碱或蔗糖替代[Na+]o以消除钠钙交换从而诱发TI的实验中，镍离子仍然会降低内向TI并增加外向TI。有无[Na+]o时镍离子的作用没有显著差异。在无[Na+]o情况下镍离子的作用证实，镍离子诱导的内向TI衰减不是由钠钙交换介导的，而是通过抑制TI通道实现的。急性暴露于锰离子（5 mmol/L）时，内向TI几乎完全消失，而此时外向TI仅略有下降。第三种二价阳离子镉离子（0.25 - 1.0 mmol/L）可同时强烈抑制内向和外向TI。镍离子对内向与外向TI的相反作用以及锰离子对内向TI的优先抑制表明，多种离子通道参与了TI的传导。4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS，10 μmol/L）和4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS，0.2 mmol/L）可阻断心脏组织中的氯离子电导，显著抑制外向TI（80±9%），但对内向TI的抑制程度较小（20±4%）。我们的结果表明，在心脏浦肯野纤维中，高[Ca2+]o诱导的TI主要通过TI通道传导，这些通道可分为两种不同类型：阳离子型和阴离子型。
