[Functional properties and cytoskeletal-dependent regulation of sodium channels in leukemia cell membranes]

The paper is devoted to membrane mechanisms of sodium influx from the extracellular medium to the cytoplasm in nonexcitable cells. With the use of patch clamp technique, the activity of non-voltage-gated ionic channels in plasma membrane of human leukemia K562 cells was examined. We have identified two types of Na-permeable channels characterized by unitary conductance of 12 pS and differing in their selectivity among monovalent cations. A relative permeability value PNa/PK was estimated for both types referred to as channels of high (HS, PNa/PK = 10) and low (LS, PNa/PK = 3) selectivity, resp. Both the channels were impermeable to bivalent cations (Ca2+, Ba2+), not blocked by tetradotoxin. Their sensitivity to amiloride was extremely low. Cytochalasin D treatment of cells resulted in a significant increase in the activity of LS Na-conducting channels. Application of exogenous gelsolin to the cytoplasmic surface of inside-out membrane patch at free Ca2+ level of 1 mkM induced a similar effect of sodium channel activation; the subsequent addition of actin reduced the channel activity up to the background level. Our results show that the cortical F-actin network plays an important role in regulating the novel family of sodium channels in nonexcitable cells. It could be assumed that the actin disassembly causes a rise in LS channel activity, whereas the actin assembly induces inactivation of the channels.