Cholesterol modulates acetylcholine receptor diffusion by tuning confinement sojourns and nanocluster stability
  Translational motion of neurotransmitter receptors is key for determining
receptor number at the synapse and hence, synaptic efficacy. We combine
live-cell STORM superresolution microscopy of nicotinic acetylcholine receptor
(nAChR) with single-particle tracking, mean-squared displacement (MSD), turning
angle, ergodicity, and clustering analyses to characterize the lateral motion
of individual molecules and their collective behaviour. nAChR diffusion is
highly heterogeneous: subdiffusive, Brownian and, less frequently,
superdiffusive. At the single-track level, free walks are transiently
interrupted by ms-long confinement sojourns occurring in nanodomains of ~36 nm
radius. Cholesterol modulates the time and the area spent in confinement.
Turning angle analysis reveals anticorrelated steps with time-lag dependence,
in good agreement with the permeable fence model. At the ensemble level,
nanocluster assembly occurs in second-long bursts separated by periods of
cluster disassembly. Thus, millisecond-long confinement sojourns and
second-long reversible nanoclustering with similar cholesterol sensitivities
affect all trajectories; the proportion of the two regimes determines the
resulting macroscopic motional mode and breadth of heterogeneity in the
ensemble population.
