CHOLESTEROL SENSITIVITY AND LIPID RAFT TARGETING OF KIR 2.1 CHANNELS

¹ University of Pennsylvania
² UNiversity of Pennsylvania
³ Cornell University
⁴ University of California - Santa Barbara
⁵ The Children's Hospital of Philadelphia, Philadelphia

^* To whom correspondence should be addressed. E-mail: ilevitan{at}mail.med.upenn.edu.

Submitted on April 2, 2004
Revised on May 12, 2004
Accepted on 21 September 2004

	Abstract

This study investigates how changes in the level of cellular cholesterol affect inwardly-rectifying K+ channels belonging to a family of strong rectifiers (Kir2). Our earlier study has shown that an increase in cellular cholesterol suppresses endogenous K+ current in vascular endothelial cells that is presumably underlied by Kir2.1 channels. Here we show that, indeed, cholesterol increase strongly suppressed whole-cell Kir2.1 current when the channels were expressed in a null cell line. However, cholesterol level had no effect on the unitary conductance and only little effect on the open probability of the channels. Inhibiting protein synthesis had no effect on the cholesterol sensitivity of Kir2.1 and no cholesterol effect was observed on the total level of Kir2.1 protein. We suggest, therefore, that cholesterol modulates not the total amount of Kir2.1 protein but the number of active channels in the membrane. Comparing the effects of cholesterol on the different members of the Kir2.x family, shows that Kir2.1 and Kir2.2 have similar high sensitivity to cholesterol, Kir2.3 is much less sensitive and Kir2.4 has an intermediate sensitivity. Finally, we show that Kir2.x channels partition virtually exclusively into triton-insoluble membrane fractions indicating that the channels are targeted into cholesterol-rich lipid rafts.

Key Words: K+ channels, cholesterol, endothelial cells, lipid rafts

This article has been cited by other articles:

				F. A. Haass, M. Jonikas, P. Walter, J. S. Weissman, Y.-N. Jan, L. Y. Jan, and M. Schuldiner Identification of yeast proteins necessary for cell-surface function of a potassium channel PNAS, November 13, 2007; 104(46): 18079 - 18084. [Abstract] [Full Text] [PDF]

				J. Abi-Char, A. Maguy, A. Coulombe, E. Balse, P. Ratajczak, J.-L. Samuel, S. Nattel, and S. N. Hatem Membrane cholesterol modulates Kv1.5 potassium channel distribution and function in rat cardiomyocytes J. Physiol., August 1, 2007; 582(3): 1205 - 1217. [Abstract] [Full Text] [PDF]

				W. F. Jackson Silent Inward Rectifier K+ Channels in Hypercholesterolemia Circ. Res., April 28, 2006; 98(8): 982 - 984. [Full Text] [PDF]

				Y. Fang, E. R. Mohler III, E. Hsieh, H. Osman, S. M. Hashemi, P. F. Davies, G. H. Rothblat, R. L. Wilensky, and I. Levitan Hypercholesterolemia Suppresses Inwardly Rectifying K+ Channels in Aortic Endothelium In Vitro and In Vivo Circ. Res., April 28, 2006; 98(8): 1064 - 1071. [Abstract] [Full Text] [PDF]

				D. J. Frankel, J. R. Pfeiffer, Z. Surviladze, A. E. Johnson, J. M. Oliver, B. S. Wilson, and A. R. Burns Revealing the Topography of Cellular Membrane Domains by Combined Atomic Force Microscopy/Fluorescence Imaging Biophys. J., April 1, 2006; 90(7): 2404 - 2413. [Abstract] [Full Text] [PDF]

				M. Toselli, G. Biella, V. Taglietti, E. Cazzaniga, and M. Parenti Caveolin-1 Expression and Membrane Cholesterol Content Modulate N-Type Calcium Channel Activity in NG108-15 Cells Biophys. J., October 1, 2005; 89(4): 2443 - 2457. [Abstract] [Full Text] [PDF]