Sterol-Dependent Nicotinic Acetylcholine Receptor Microdomains At The Plasma Membrane: Structural , Functional And Pathological Implications.

BARRANTES FRANCISCO,; THORSTEN LANG,; BAIER JAVIER,; BONINI IDA,; INGRID GARBUS

Asilomar, California

Congreso; 48th annual meeting of the biophysical society; 2004

biophysical society

The relationship between lipid domains and acetylcholine receptor (AChR) is currently being characterizedin our laboratory using mammalian cells expressing neuronal or muscle AChR and a combination offluorescence microscopy, various lipid modification procedures, and single-channel recording. Changes incell-surface bungarotoxin (BTX) fluorescence are observed upon cholesterol (Chol) and sphingolipidmodification, and correlated with modification of AChR targeting to the cell-surface and with changes inthe physical state of the plasmalemma in various mammalian AChR-expressing cells. Chol content inpurified plasma membrane fractions is drastically reduced by acute (methyl-beta-cyclodextrin (CDx))treatment. Reversibility was accomplished by Chol-CDx mediated Chol replenishment. CDx reduced BTXfluorescence at the surface of intact cells and in single plasma membrane sheets. The latter findingindicates that the decrease of fluorescent-labeled AChR upon Chol depletion occurs directly at the cellmembrane, where BTX fluorescence is concentrated in small, submicron-sized fluorescent spots that areinterpreted as AChR microdomains. Patch-clamp studies reveal that Chol depletion increases open channelprobability and channel open time, whereas Chol enrichment has the opposite effect. Our currenthypothesis is that sterols at the plasmalemma may be homeostatically controlled within critical levels andexert a modulatory fine-tuning of AChR function. Misbalance may contribute to pathological conditions, asmay be observed in abnormal beta-amyloid interaction with neuronal AChRs.