Chinet T C, Fullton J M, Yankaskas J R, Boucher R C, Stutts M J
School of Medicine, University of North Carolina, Chapel Hill 27599-7020.
Am J Physiol. 1993 Oct;265(4 Pt 1):C1050-60. doi: 10.1152/ajpcell.1993.265.4.C1050.
We used patch-clamp techniques to study the channels that underlie the Na+ conductance of the apical membrane of human normal nasal epithelial cells. Cells were cultured on permeable supports and studied after confluence. In 172 of 334 (52%) excised membrane patches, we observed 20-pS Na(+)-permeable channels that do not discriminate between Na+ and K+ (pNa/pK = 1.33). These nonselective cation channels contained subpopulations that differed by dependence of open probability on voltage and bath Ca2+ activity, suggesting two or more channel types with similar electrical properties. In the presence of 10(-4) M amiloride in the pipette, the proportion of excised patches with nonselective cation channels decreased to 52 of 139 patches (37%), but the decrease was spread across all subpopulations of nonselective cation channels in excised patches. Thus no distinctive Na(+)-selective amiloride-sensitive channels were identified in excised patches. In cell-attached patches, Na(+)-permeable channels were recorded in 56 of 262 patches (21%). Their conductance was 21.4 +/- 1.5 pS (n = 25), and most were selective for Na+ over K+ (pNa/pK > 6). In the presence of amiloride (10(-4) M) in the pipette, the frequency of lambda Na(+)-permeable channels in cell-attached patches decreased to 8 of 134 patches (6%), revealing a population of Na(+)-selective channels recorded in cell-attached patches that was inhibited by amiloride. We conclude that, in excised patches, Na(+)-permeable channels are nonselective for Na+ over K+ and < 30% appear to be amiloride sensitive. In contrast, in cell-attached patches, most channels that conduct sodium are 1) selective for Na+ over K+ and 2) amiloride sensitive. Although we have not discovered the explanation for the discrepancy between cell-attached and excised patch data, we speculate that the channels recognized on cell account for the amiloride-sensitive Na+ conductance of the apical membrane, whereas the excision process alters the properties of the Na(+)-permeable channels and/or activate new channels.
我们运用膜片钳技术研究了人正常鼻上皮细胞顶端膜钠电导所涉及的通道。细胞培养于可渗透支持物上，汇合后进行研究。在334个切除的膜片中，有172个（52%）观察到20皮西门子（pS）的钠通透通道，这些通道对钠和钾不具有选择性（pNa/pK = 1.33）。这些非选择性阳离子通道包含不同亚群，其开放概率对电压和胞外钙离子活性的依赖性有所不同，提示存在两种或更多具有相似电学特性的通道类型。当移液管中存在10⁻⁴ M氨氯吡脒时，含有非选择性阳离子通道的切除膜片比例降至139个膜片中的52个（37%），但这种降低在切除膜片中的所有非选择性阳离子通道亚群中均有体现。因此，在切除膜片中未鉴定出明显的钠选择性氨氯吡脒敏感通道。在细胞贴附膜片中，262个膜片中的56个（21%）记录到钠通透通道。其电导为21.4 ± 1.5 pS（n = 25），且大多数对钠的选择性高于钾（pNa/pK > 6）。当移液管中存在氨氯吡脒（10⁻⁴ M）时，细胞贴附膜片中钠通透通道的频率降至134个膜片中的8个（6%），揭示出细胞贴附膜片中存在一群被氨氯吡脒抑制的钠选择性通道。我们得出结论，在切除膜片中，钠通透通道对钠和钾不具有选择性，且< 30%的通道似乎对氨氯吡脒敏感。相比之下，在细胞贴附膜片中，大多数传导钠的通道1）对钠的选择性高于钾，2）对氨氯吡脒敏感。尽管我们尚未找到细胞贴附与切除膜片数据差异的解释，但我们推测细胞上识别的通道构成了顶端膜氨氯吡脒敏感的钠电导，而切除过程改变了钠通透通道的特性和/或激活了新的通道。
