Properties of lipid microdomains in a muscle cell membrane visualized by single molecule microscopy

摘要

The lateral motion of single fluorescence labeled lipid molecules was imaged in native cell membranes on a millisecond time scale and with positional accuracy of ∼50 nm, using ‘single dye tracing’. This first application of single molecule microscopy to living cells rendered possible the direct observation of lipid-specific membrane domains. These domains were sensed by a lipid probe with saturated acyl chains as small areas in a liquid-ordered phase: the probe showed confined but fast diffusion, with high partitioning (∼100-fold) and long residence time (∼13 s). The analogous probe with mono-unsaturated chains diffused predominantly unconfined within the membrane. With ∼15 saturated probes per domain, the locations, sizes, shapes and motions of individual domains became clearly visible. Domains had a size of 0.7 μm (0.2–2 μm), covering ∼13% of total membrane area. Both the liquid-ordered phase characteristics and the sizes of domains match properties of membrane fractions described as detergent-resistant membranes (DRMs), strongly suggesting that the domains seen are the in vivo correlate of DRMs and thus may be identified as lipid rafts.