FUNCTIONAL PROPERTIES OF SODIUM CHANNELS IN CHOLESTEROL-DEPLETED K562 CELLS
A. V. Sudarikova,1 V. I. Chubinskij-Nadezhdin, Y. A. Negulyaev, E. A. Morachevskaya
Institute of Cytology RAS, St. Petersburg;
1 e-mail: nastya@mail.cytspb.rssi.ru
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.
Key words: plasma membrane, sodium channels, cytoskeleton, actin, cholesterol, human leukaemia
cells, cytochalasin, methyl-beta-cyclodextrin
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