[Functional properties of sodium channels in cholesterol-depleted K562 cells]

The level of cellular cholesterol is known to determine functional compartmentalization of membrane lipids into ordered microdomains (rafts). Lipid rafts are assumed to play an essential role in the interactions between cell membrane and cortical cytoskeleton. As we have shown earlier, the activity of non-voltage-gated sodium channels in K562 human leukaemia cells is critically dependent on actin cytoskeleton organization. In the present paper, functional properties of sodium channels in K562 cells were examined after cholesterol-depleting treatment using methyl-beta-cyclodextrin (MbCD), selective acceptor of sterols. Single currents through sodium channels were recorded in cell-attached and inside-out mode experiments with the use of patch clamp technique. After incubation with MbCD (2.5 or 5.0 mM), an activation of sodium channels in response to cytochalasin B or D was observed in membrane fragments as well as in native cells. Characteristics of the channels in cholesterol-depleted K562 cells were similar to those in control; unitary conductance was 12 pS. Inside-out experiments with the use of globular actin have indicated that filament assembly on cytoplasmic membrane side causes an inactivation of sodium channels. These data imply that there is no association of sodium channels with cholesterol-rich membrane microdomains in K562 cells. Possible mechanisms underlying an interplay between plasma membrane and cortical cytoskeleton are discussed.