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Abstract

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^- = B_r^- >> 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 K_I = 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.