Ruknudin A, Sachs F, Bustamante J O
Department of Biophysical Sciences, State University of New York, Buffalo 14214.
Am J Physiol. 1993 Mar;264(3 Pt 2):H960-72. doi: 10.1152/ajpheart.1993.264.3.H960.
With use of single-channel patch-clamp recording, we found five distinct types of stretch-activated ion channels (SACs) in tissue-cultured embryonic chick cardiac myocytes. With 140 mM K+ saline in the pipette, four channels had linear conductances of approximately equal to 25, 50, 100, and 200 pS and other channel was an inward rectifier of approximately equal to 25 pS at 0 mV membrane potential. The 100- and 200-pS channels were K+ selective, whereas the others passed alkali cations and Ca2+. From reversal potentials, the permeability ratio of K+/Na+, PK/PNa, was 3-7 for nonselective channels and 7-16 for K(+)-selective channels. Channel density was approximately equal to 0.3/microns2 for linear conductances and approximately equal to 0.1/microns2 for inward rectifier. Open-channel noise was a function of pipette filling solution with root-mean-square (RMS) noise increasing in the order K+ < isosmotic sucrose (plus trace ions) < Na+, probably reflecting short-lived block by extracellular ions. All channels were blocked by 20 microM Gd3+. The 25-pS linear channel was also blocked by 12.5 microM tetrodotoxin and 10 microM diltiazem, but the others were insensitive at these concentrations. Extracellular Cs+ and tetraethylammonium chloride did not block any channels. We saw no SAC activity in cells grown without embryo extract (EE), which demonstrates that channel expression, or some necessary cofactor, is under control of growth factors. Basic fibroblast growth factor (FGF) could replace EE in supporting channel expression. The presence of SACs capable of generating inward currents might explain how stretch increases automaticity in the heart. Because some SACs were permeable to Ca2+, they could contribute to the Starling curve and perhaps to initiating stretch-induced hypertrophy.
通过使用单通道膜片钳记录技术，我们在组织培养的胚胎鸡心肌细胞中发现了五种不同类型的牵张激活离子通道（SACs）。当移液管中使用140 mM K⁺ 盐溶液时，四种通道的线性电导分别约为25、50、100和200 pS，另一种通道在膜电位为0 mV时是一个约25 pS的内向整流器。100 pS和200 pS的通道对K⁺ 具有选择性，而其他通道则允许碱金属阳离子和Ca²⁺ 通过。根据反转电位，非选择性通道的K⁺/Na⁺ 渗透率比PK/PNa为3 - 7，K⁺ 选择性通道的该渗透率比为7 - 16。线性电导通道的通道密度约为0.3/μm²，内向整流器的通道密度约为0.1/μm²。开放通道噪声是移液管填充溶液的函数，均方根（RMS）噪声按K⁺ < 等渗蔗糖（加微量离子）< Na⁺ 的顺序增加，这可能反映了细胞外离子的短暂阻断。所有通道都被20 μM Gd³⁺ 阻断。25 pS的线性通道也被12.5 μM河豚毒素和10 μM地尔硫䓬阻断，但其他通道在这些浓度下不敏感。细胞外Cs⁺ 和四乙铵氯化物不阻断任何通道。在没有胚胎提取物（EE）的情况下生长的细胞中我们未观察到SAC活性，这表明通道表达或某些必需的辅助因子受生长因子的控制。碱性成纤维细胞生长因子（FGF）可以替代EE来支持通道表达。能够产生内向电流的SACs的存在可能解释了牵张如何增加心脏的自律性。因为一些SACs对Ca²⁺ 具有通透性，它们可能对斯塔林曲线有贡献，也许还对引发牵张诱导的肥大有贡献。
