Poly(ethylene glycol)-Cholesterol inhibits l-type Ca 2+ channel currents and augments voltage-dependent inactivation in A7r5 cells

Abstract

Cholesterol distributes at a high density in the membrane lipid raft and modulates ion channel currents. Poly(ethylene glycol) cholesteryl ether (PEG-cholesterol) is a nonionic amphipathic lipid consisting of lipophilic cholesterol and covalently bound hydrophilic PEG. PEG-cholesterol is used to formulate lipoplexes to transfect cultured cells, and liposomes for encapsulated drug delivery. PEG-cholesterol is dissolved in the external leaflet of the lipid bilayer, and expands it to flatten the caveolae and widen the gap between the two leaflets. We studied the effect of PEG-cholesterol on whole cell L-type Ca2+ channel currents (ICa,L) recorded from cultured A7r5 arterial smooth muscle cells. The pretreatment of cells with PEGcholesterol decreased the density of ICa,L and augmented the voltage-dependent inactivation with acceleration of time course of inactivation and negative shift of steady-state inactivation curve. Methyl- b-cyclodextrin (MbCD) is a cholesterolbinding oligosaccharide. The enrichment of cholesterol by the MbCD:cholesterol complex (cholesterol (MbCD)) caused inhibition of ICa,L but did not augment voltage-dependent inactivation. Incubation with MbCD increased ICa,L, slowed the time course of inactivation and shifted the inactivation curve to a positive direction. Additional pretreatment by a high concentration of MbCD of the cells initially pretreated with PEG-cholesterol, increased ICa,L to a greater level than the control, and removed the augmented voltage-dependent inactivation. Due to the enhancement of the voltage-dependent inactivation, PEG-cholesterol inhibited window I Ca,L more strongly as compared with cholesterol (MbCD). Poly(ethylene glycol) conferred to cholesterol the efficacy to induce sustained augmentation of voltage-dependent inactivation of ICa,L.