Dun Wen, Boyden Penelope A
Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, New York, NY, USA.
Am J Physiol Heart Circ Physiol. 2005 Aug;289(2):H667-73. doi: 10.1152/ajpheart.00180.2005. Epub 2005 Apr 8.
We have shown reduced density and altered kinetics in slowly activating K+ currents (I(Ks)) in epicardial border zone (EBZ) cells (IZs) of the 5-day-infarcted canine heart (Jiang M, Cabo, C, Yao J-A, Boyden PA, and Tseng G-N. Cardiovasc Res 48: 34-43, 2000). beta-Adrenergic stimulation with isoproterenol increases I(Ks) in normal cells (NZs). In this study, we used a voltage-clamp protocol with an external solution to isolate I(Ks) from contaminating currents to determine the effects of 1 muM isoproterenol on I(Ks) in IZs and NZs. Under our recording conditions, 10 microM azimilide-sensitive currents were stimulated with isoproterenol to compare responsiveness of I(Ks) to isoproterenol in the two cell groups. I(Ks) tail density was reduced 67% in IZs (group I, n = 26) compared with NZs (n = 24, P < 0.05). Isoproterenol-stimulated azimilide-sensitive tail currents were increased 1.72 +/- 0.2-fold in NZs and 2.2 +/- 0.3-fold in IZs (P > 0.05). In 33% of IZs (group II, n = 13), native currents showed no tail currents; however, isoproterenol-stimulated azimilide-sensitive currents were voltage dependent, fast activating, and large in amplitude compared with group I IZs, similar to "lone" KCNQ1 currents. Using short clamp pulses, we also found an increase in sustained currents sensitive to tetraethylammonium chloride (TEA) and no change in C-9356-sensitive currents in IZs with little or no transient outward current. In some IZs where I(Ks) is downregulated, the effect of isoproterenol on I(Ks) was similar to that on I(Ks) in NZs. In others, the existence of lone KCNQ1-type currents, which are sensitive to beta-adrenergic stimulation, is consistent with our findings of an increased KCNQ1-to-KCNE1 mRNA ratio (Jiang et al.). Accompanying altered I(Ks) in IZs are an enhanced TEA-sensitive current and a normal C-9356-sensitive current.
我们已经证实在梗死后5天的犬心的心外膜边缘区(EBZ)细胞(IZs)中,缓慢激活的钾电流(I(Ks))密度降低且动力学改变(Jiang M、Cabo C、Yao J-A、Boyden PA和Tseng G-N。《心血管研究》48: 34 - 43,2000)。用异丙肾上腺素进行β-肾上腺素能刺激可增加正常细胞(NZs)中的I(Ks)。在本研究中,我们使用一种电压钳制方案及外部溶液来将I(Ks)与污染电流分离,以确定1μM异丙肾上腺素对IZs和NZs中I(Ks)的影响。在我们的记录条件下,用异丙肾上腺素刺激10μM阿齐米利特敏感电流,以比较两个细胞组中I(Ks)对异丙肾上腺素的反应性。与NZs(n = 24,P < 0.05)相比,IZs(第I组,n = 26)中的I(Ks)尾电流密度降低了67%。异丙肾上腺素刺激的阿齐米利特敏感尾电流在NZs中增加了1.72±0.2倍,在IZs中增加了2.2±0.3倍(P > 0.05)。在33%的IZs(第II组,n = 13)中,天然电流未显示尾电流;然而,与第I组IZs相比,异丙肾上腺素刺激的阿齐米利特敏感电流呈电压依赖性、快速激活且幅度较大,类似于“孤立的”KCNQ1电流。使用短钳制脉冲,我们还发现对四乙铵(TEA)敏感的持续电流增加,而在几乎没有或没有瞬时外向电流的IZs中,对C - 9356敏感的电流没有变化。在一些I(Ks)下调的IZs中,异丙肾上腺素对I(Ks)的作用与对NZs中I(Ks)的作用相似。在其他情况下,存在对β-肾上腺素能刺激敏感的孤立KCNQ1型电流,这与我们关于KCNQ1与KCNE1 mRNA比值增加的发现(Jiang等人)一致。伴随IZs中I(Ks)的改变,是增强的对TEA敏感的电流和正常的对C - 9356敏感的电流。