Lipid vesicle-mediated alterations of membrane cholesterol levels: Effects on Na+ and K+ currents in squid axon |
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Authors: | Joy A Steele Mark J Poznansky Douglas C Eaton Malcolm S Brodwick |
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Institution: | (1) Marine Biological Laboratories, Woods Hole, Massachusetts;(2) Present address: Department of Physiology, University of Alberta, Edmonton, Alberta;(3) Present address: Clamp Division, Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas |
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Abstract: | Summary We demonstrate that cholesterol can exchange from sonicated lipid vesicles to a perfused squid giant axon membrane and that vesicles with varying cholesterol/phospholipid (C/P) mole ratios can be used to achieve either net loading or net depletion of axon membrane cholesterol. Two types of evidence were obtained which show that net loading or depletion of cholesterol was achieved: (i) changes in the cholesterol/phospholipid (C/P) mole ratios of axons, and (ii) visualization of cholesterol depleted from the preparation by cholesterol-free vesicles by thin-layer chromatography. The C/P mole ratios indicate that cholesterol levels in the preparation were increased or decreased by 30–40%. Increasing or decreasing membrane cholesterol levels were ineffective in altering the Na+ or K+ occurrents in voltage-clamped axons. In addition, we determined that cholesterol flip-flop across the axonal membrane occurred with at
1/2 of 7.3 to 15.3 min. |
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Keywords: | Cholesterol exchange membrane lipids squid axon ionic conductances flip-flop lipid vesicles |
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