Premium
Cells defective in sphingolipids biosynthesis express low amounts of muscle nicotinic acetylcholine receptor
Author(s) -
Roccamo A. M.,
Pediconi M. F.,
Aztiria E.,
Zanello L.,
Wolstenholme A.,
Barrantes F. J.
Publication year - 1999
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1999.00574.x
Subject(s) - chinese hamster ovary cell , transfection , acetylcholine receptor , microbiology and biotechnology , biochemistry , cell culture , chemistry , biology , receptor , gene , genetics
Abstract The properties of the nicotinic acetylcholine receptor (AChR) are modulated by its lipid microenvironment. Studies of such modulation are hampered by the cell's homeostatic mechanisms that impede sustained modification of membrane lipid composition. We have devised a novel strategy to circumvent this problem and study the effect of changes in plasma membrane lipid composition on the functional properties of AChR. This approach is based on the stable transfection of AChR subunit cDNAs into cells defective in a specific lipid metabolic pathway. In the present work we illustrate this new strategy with the successful transfection of a temperature‐sensitive Chinese hamster ovary (CHO) cell line, SPB‐1, with the genes corresponding to the four adult mouse AChR subunits. The new clone, SPB‐1/SPH, carries a mutation of the gene coding for serine palmitoyl transferase, the enzyme that catalyses the first step in sphingomyelin (Sph) biosynthesis. This defect causes a decrease of Sph de novo synthesis at non‐permissive temperatures. The IC 50 for inhibition of α‐BTX binding with the agonist carbamoylcholine exhibited values of 3.6 and 2.7 μ m in the wild‐type and Sph‐deficient cell lines, respectively. The corresponding IC 50 values for the competitive antagonist d ‐tubocurarine ( d ‐TC) were 2.8 and 3.4 μ m , respectively. No differences in single‐channel properties were observed between wild‐type and mutant cell lines grown at the non‐permissive, lipid defect‐expressing temperature using the patch‐clamp technique. Both cells exhibited two open times with mean values of 0.35 ± 0.05 and 1.78 ± 0.2 ms at 12 °C. Taken together, these results suggest that the AChR is expressed as the complete heteroligomer. However, only 10–20% of the total AChR synthesized reached the surface membrane in the mutant cell line and exhibited a higher metabolic turnover, with a half‐life about 50% shorter than the wild‐type cells. When control CHO‐K1/A5 cells were treated with fumonisin B1, an inhibitor of sphingosine (sphinganine) N‐acetyltransferase (ceramide synthase), a 45.5% decrease in cell surface AChR expression was observed. The results suggest that sphingomyelin deficiency conditions AChR targeting to the plasma membrane.