Rettinger J, Schwarz W
Max-Planck-Institut für Biophysik, Frankfurt/Main, Germany.
J Basic Clin Physiol Pharmacol. 1994 Jan-Mar;5(1):27-44. doi: 10.1515/jbcpp-1994-050103. Epub 2025 Apr 10.
Four types of ion-selective channels were found by the patch-clamp technique in the human erythroleukemia K562 cells. I) in cell-attached configuration at potentials less negative than -40 mV an 8 ps channel was detected. The potential dependence of channel activity suggests that this is the TTX-sensitive Na+ channel. II) A cation-selective channel was observed with equal permeability for Na+ and K+ and a potential-independent single-channel conductance of 19 pS. The channel is activated by intracellular Ca2+ and inhibited by TEA, III) A predominantly anion-selective channel was identified with the selectivity sequence NO3- > J- > Cl- = Br- >> SO4(2-). The single-channel conductance shows outward rectification, and is in symmetrical NaCl solution 19 pS at -60 mV and 54pS at +50 mV. The open- and closed-time distributions suggest one open and at least four closed states. At submicromolar concentrations, the open state is blocked by H2DIDS leading to channel flicker between open and blocked channel; higher concentrations (apparent KI = 6.8 uM) lead to a longer-lasting blocked state. Both components of inhibition are reversible. IV) In addition, an 8 pS, Na(+)- and K(+)- selective channel could be induced by application of palytoxin. For channel activity, the presence of extracellular Na+ is essential. It is assumed that the Na+, K(+)-pump molecule is involved in the channel formation. Similarly, it is discussed whether the anion-selective channel represents a pore conformation of an electrically silent anion exchanger.
通过膜片钳技术在人红白血病K562细胞中发现了四种离子选择性通道。I）在细胞贴附模式下，当电位低于 -40 mV时，检测到一个8 pS的通道。通道活性的电位依赖性表明这是TTX敏感的Na⁺通道。II）观察到一种阳离子选择性通道，对Na⁺和K⁺具有相同的通透性，单通道电导为19 pS且与电位无关。该通道被细胞内Ca²⁺激活并被TEA抑制。III）鉴定出一种主要为阴离子选择性的通道，其选择性顺序为NO₃⁻ > I⁻ > Cl⁻ = Br⁻ >> SO₄²⁻。单通道电导表现出外向整流，在对称NaCl溶液中，-60 mV时为19 pS，+50 mV时为54 pS。开放和关闭时间分布表明有一个开放状态和至少四个关闭状态。在亚微摩尔浓度下，开放状态被H2DIDS阻断，导致通道在开放和阻断通道之间闪烁；更高浓度（表观KI = 6.8 μM）导致更长时间的阻断状态。两种抑制成分都是可逆的。IV）此外，应用岩沙海葵毒素可诱导出一个8 pS的Na⁺和K⁺选择性通道。对于通道活性，细胞外Na⁺的存在至关重要。推测Na⁺, K⁺ -泵分子参与了通道形成。同样，也讨论了阴离子选择性通道是否代表电沉默阴离子交换器的孔构象。
