Ion-Selective Channels in K562 Cells: A Patch-Clamp Analysis.

Abstract

Four types of ion-selective channels were found by the patch-clamp technique in the human erythroleucemia 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. ΙΠ)A predominantly anion-selective channel was identified with the selectivity sequence N03" >J" > G" = Br » S04 2·. The single-channel conductance shows outward rectification, and is in symmetrical NaCl solution 19 pS at -60 mV and 54 pS at +50 mV. The open- and closedtime 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 Kj=6.8 μΜ) 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 anionselective channel represents a pore conformation of an electrically silent anion exchanger.