Heterogeneous distribution of acetylcholine receptors in chick myocytes induced by cholesterol enrichment

Lasalde, José A.; Colom, A.; Resto, Edgard; Zuazaga, C.

doi:10.1016/0005-2736(95)80025-b

Cited by 12 publications

(7 citation statements)

References 26 publications

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“…The cholesterol inhibition of nAChR functionality is a central aspect of this study. There is a limited amount of studies that have examined the effects of cholesterol enrichment on nAChR function in cell membrane models (Lechleiter et al 1986; Lasalde et al 1995; Antollini and Barrantes 1998; Santiago et al 2001; Barrantes 2002, 2004). …”

Section: Discussionmentioning

confidence: 99%

Heterogeneous Inhibition in Macroscopic Current Responses of Four Nicotinic Acetylcholine Receptor Subtypes by Cholesterol Enrichment

et al. 2016

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The nicotinic acetylcholine receptor (nAChR), located in the cell membranes of neurons and muscle cells, mediates the transmission of nerve impulses across cholinergic synapses. In addition, the nAChR is also found in the electric organs of electric rays (e.g., the genus Torpedo). Cholesterol, which is a key lipid for maintaining the correct functionality of membrane proteins, has been found to alter the nAChR function. We were thus interested to probe the changes in the functionality of different nAChRs expressed in a model membrane with modified cholesterol to phospholipid ratios (C/P). In this study, we examined the effect of increasing the C/P ratio in Xenopus laevis oocytes expressing the neuronal α7, α4β2, muscle-type, and Torpedo californica nAChRs in their macroscopic current responses. Using the two-electrode voltage clamp technique, it was found that the neuronal α7 and Torpedo nAChRs are significantly more sensitive to small increases in C/P than the muscle-type nAChR. The peak current versus C/P profiles during enrichment display different behaviors; α7 and Torpedo nAChRs display a hyperbolic decay with two clear components, whereas muscle-type and α4β2 nAChRs display simple monophasic decays with different slopes. This study clearly illustrates that a physiologically relevant increase in membrane cholesterol concentration produces a remarkable reduction in the macroscopic current responses of the neuronal α7 and Torpedo nAChRs functionality, whereas the muscle nAChR appears to be the most resistant to cholesterol inhibition among all four nAChR subtypes. Overall, the present study demonstrates differential profiles for cholesterol inhibition among the different types of nAChR to physiological cholesterol increments in the plasmatic membrane. This is the first study to report a cross-correlation analysis of cholesterol sensitivity among different nAChR subtypes in a model membrane.

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Section: Discussionmentioning

confidence: 99%

Heterogeneous Inhibition in Macroscopic Current Responses of Four Nicotinic Acetylcholine Receptor Subtypes by Cholesterol Enrichment

et al. 2016

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“…Individual amino acid mutations in the M4 AChR TM domain modulate AChR function (Lee et al 1994;Lasalde et al 1996;Ortiz-Miranda et al 1997;Bouzat et al 1998;Tamamizu et al 1999Tamamizu et al , 2000, a clear indication that AChR function is effectively influenced by M4 (reviewed in Barrantes 2004), the only member of the outermost TM ''ring'' (Barrantes 2003). Furthermore, changes in membrane lipid composition (Criado et al 1984;Sunshine & McNamee 1994;Baenziger et al 2000;daCosta et al 2002) and/or presence of exogenous hydrophobic molecules (Andreasen & McNamee 1980;Villar et al 1988;Bouzat & Barrantes 1993a,b, 1996Lasalde et al 1995;Nurowska & Ruzzier 1996;Blanton et al 1999;Santiago et al 2001;Garbus et al 2001Garbus et al , 2002 also affect AChR function. Changes in AChR lipid microenvironment could induce hydrophobic mismatch between the hydrophobic TM segments and the hydrophobic width of the bilayer, as revealed here in the series of experiments on Chol addition.…”

Section: Discussionmentioning

confidence: 99%

Fluorescence and molecular dynamics studies of the acetylcholine receptor γM4 transmembrane peptide in reconstituted systems

Antollini

Jiang³

et al. 2005

Molecular Membrane Biology

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A combination of fluorescence spectroscopy and molecular dynamics (MD) is applied to assess the conformational dynamics of a peptide making up the outermost ring of the nicotinic acetylcholine receptor (AChR) transmembrane region and the effect of membrane thickness and cholesterol on the hydrophobic matching of this peptide. The fluorescence studies exploit the intrinsic fluorescence of the only tryptophan residue in a synthetic peptide corresponding to the fourth transmembrane domain of the AChR gamma subunit (gammaM4-Trp(6)) reconstituted in lipid bilayers of varying thickness, and combine this information with quenching studies using depth-sensitive phosphatidylcholine spin-labeled probes and acrylamide, polarization of fluorescence, and generalized polarization of Laurdan. A direct correlation was found between bilayer width and the depth of insertion of Trp(6). We further extend our recent MD study of the conformational dynamics of the AChR channel to focus on the crosstalk between M4 and the lipid-belt region. The isolated gammaM4 peptide is shown to possess considerable orientational flexibility while maintaining a linear alpha-helical structure, and to vary its tilt depending on bilayer width and cholesterol (Chol) content. MD studies also show that gammaM4 also establishes contacts with the other TM peptides on its inner face, stabilizing a shorter TM length that is still highly sensitive to the lipid environment. In the native membrane the topology of the M4 ring is likely to exhibit a similar behavior, dynamically modifying its tilt to match the hydrophobic thickness of the bilayer.

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“…The incubated oocytes were then washed three times with a total volume of 3 ml of MOR2. The cholesterol/ phospholipid (C/P) molar ratio of the plasma membrane of the oocytes was estimated using protocols as described (23,24) with minor modification as described (27,28). This method increased the cholesterol phospholipid molar ratio of plasma membrane of the oocyte from 0.51 Ϯ 0.1 (control) to 0.87 Ϯ 0.06 (n ϭ 90 oocytes in six batches of oocytes).…”

Section: Methodsmentioning

confidence: 99%

Probing the Effects of Membrane Cholesterol in the Torpedo californica Acetylcholine Receptor and the Novel Lipid-exposed Mutation αC418W in XenopusOocytes

Santiago¹,

Guzmán²,

Rojas³

et al. 2001

Journal of Biological Chemistry

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The effects of cholesterol on the ion-channel function of the Torpedo acetylcholine receptor (nAChR) and the novel lipid-exposed gain in function ␣C418W mutation have been investigated in Xenopus laevis oocytes. We found conditions to increase the cholesterol/phospholipid (C/P) molar ratio on the plasma membrane of Xenopus oocytes from 0.5 to 0.87, without significant physical damage or change in morphology to the oocytes. In addition, we developed conditions to deplete endogenous cholesterol from oocytes using a methyl-␤-cyclodextrin incubation procedure without causing membrane instability of the cells. Methyl-␤-cyclodextrin was also used to examine the reversibility of the inhibitory effect of cholesterol on AChR function. Depletion of 43% of endogenous cholesterol from oocytes (C/P ‫؍‬ 0.3) did not show any significant change in macroscopic response of the wild type, whereas in the ␣C418W mutant the same cholesterol depletion caused a dramatic gainin-function response of this lipid-exposed mutation in addition to the increased response caused by the mutation itself. Increasing the C/P ratio to 0.87 caused an inhibition of the macroscopic response of the Torpedo wild type of about 52%, whereas the ␣C418W mutation showed an 81% inhibition compared with the responses of control oocytes. The wild type receptor did not recover from this inhibition when the excess cholesterol was depleted to near normal C/P ratios; however, the ␣C418W mutant displayed 63% of the original current, which indicates that the inhibition of this lipid-exposed mutant was significantly reversed. The ability of the ␣C418W mutation to recover from the inhibition caused by cholesterol enrichment suggests that the interaction of cholesterol with this lipid-exposed mutation is significantly different from that of the wild type. The present data demonstrate that a single lipid-exposed position in the AChR could alter the modulatory effect of cholesterol on AChR function.

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Heterogeneous distribution of acetylcholine receptors in chick myocytes induced by cholesterol enrichment

Cited by 12 publications

References 26 publications

Heterogeneous Inhibition in Macroscopic Current Responses of Four Nicotinic Acetylcholine Receptor Subtypes by Cholesterol Enrichment

Heterogeneous Inhibition in Macroscopic Current Responses of Four Nicotinic Acetylcholine Receptor Subtypes by Cholesterol Enrichment

Fluorescence and molecular dynamics studies of the acetylcholine receptor γM4 transmembrane peptide in reconstituted systems

Probing the Effects of Membrane Cholesterol in the Torpedo californica Acetylcholine Receptor and the Novel Lipid-exposed Mutation αC418W in XenopusOocytes

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