Near-membrane dynamics and capture of TRPM8 channels within transient confinement domains.
BACKGROUND
The cold and menthol receptor, TRPM8, is a non-selective cation channel expressed in a subset of peripheral neurons that is responsible for neuronal detection of environmental cold stimuli. It was previously shown that members of the transient receptor potential (TRP) family of ion channels are translocated toward the plasma membrane (PM) in response to agonist stimulation. Because the spatial and temporal dynamics of cold receptor cell-surface residence may determine neuronal activity, we hypothesized that the movement of TRPM8 to and from the PM might be a regulated process. Single particle tracking (SPT) is a useful tool for probing the organization and dynamics of protein constituents in the plasma membrane.


RESULTS
We used SPT to study the receptor dynamics and describe membrane/near-membrane behavior of particles containing TRPM8-EGFP in transfected HEK-293T and F-11 cells. Cells were imaged using total internal reflection fluorescence (TIRF) microscopy and the 2D and 3D trajectories of TRPM8 molecules were calculated by analyzing mean-square particle displacement against time. Four characteristic types of motion were observed: stationary mode, simple Brownian diffusion, directed motion, and confined diffusion. In the absence of cold or menthol to activate the channel, most TRPM8 particles move in network covering the PM, periodically lingering for 2-8 s in confined microdomains of about 800 nm radius. Removing cholesterol with methyl-beta-cyclodextrin (MβCD) stabilizes TRPM8 motion in the PM and is correlated with larger TRPM8 current amplitude that results from an increase in the number of available channels without a change in open probability.


CONCLUSIONS
These results reveal a novel mechanism for regulating TRPM8 channel activity, and suggest that PM dynamics may play an important role in controlling electrical activity in cold-sensitive neurons.
Instituto de Fisiologia, Facultad de Medicina, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile.
Luis A
LA
Veliz
Carlos A
CA
Toro
Juan P
JP
Vivar
Luis A
LA
Arias
Jenifer
J
Villegas
Maite A
MA
Castro
Sebastian
S
Brauchi
D002460:Cell Line; D002784:Cholesterol / Q000737:chemistry / Q000302:isolation & purification; D006801:Humans; D008856:Microscopy, Fluorescence; D050053:TRPM Cation Channels / Q000378:metabolism*; D047392:beta-Cyclodextrins / Q000737:chemistry
D050053:TRPM Cation Channels; C425966:TRPM8 protein, human; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol