Molecular and functional identification of sodium channels in K562 cells

Abstract

Modulations of ion channel activity underlie rapid changes in membrane transport of cations in various non-excitable cells. Previously, in smooth muscle cells, macrophages, lymphocytes, carcinoma and leukemia cell lines, non-voltage-gated sodium (NVGS) channels have been found. The activity of NVGS channels was shown to be critically dependent on the organization of actin cytoskeleton. The molecular identity of NVGS channels remains unclear. The present work is focused on molecular and functional identification of NVGS channels in human myeloid leukemia K562 cells. Degenerin/epithelial Na+ channels (DEG/ENaC) could be considered as a possible molecular correlates. Using RT-PCR, expression of alpha-, beta-, gamma-hENaC subunits in K562 cells was detected. Various modes of the patch-clamp method were employed to examine functional properties of sodium channels, specifically, to test the effect of amiloride on single channel and integral currents. Biophysical characteristics of NVSG channels were close to ENaC; the channels have unitary conductance 12 pS (145 mM Na+) and were impermeable for divalent cations (Ca2+ and Mg2+). We found that amiloride did not inhibit NVGS channels. Importantly, no amiloride-blockable sodium current was detected in the plasma membrane of K562 cells. Taken together, our observations suggest that amiloride-insensitive sodium channels in K562 cells belong to the ENaC family.