Mechanosensitive channel activity and F-actin organization in cholesterol-depleted human leukaemia cells

This study focuses on the functional role of cellular cholesterol in the regulation of mechanosensitive cation channels activated by stretch in human leukaemia K562 cells. The patch-clamp method was employed to examine the effect of methyl-beta-cyclodextrin (MbetaCD), a synthetic cholesterol-sequestering agent, on stretch-activated single currents. We found that cholesterol-depleting treatment with MbetaCD resulted in a suppression of the activity of mechanosensitive channels without a change in the unitary conductance. The probability that the channel was open significantly decreased after treatment with MbetaCD. Fluorescent microscopy revealed F-actin reorganization, possibly involving actin assembly, after incubation of the cells with MbetaCD. We suggest that suppression of mechanosensitive channel activation in cholesterol-depleted leukaemia cells is due to F-actin rearrangement, presumably induced by lipid raft destruction. Our observations are consistent with the notion that stretch-activated cation channels in eukaryotic cells are regulated by the membrane-cytoskeleton complex rather than by tension developed purely in the lipid bilayer.