Lipid microdomains and k(+) channel compartmentation: detergent and non-detergent-based methods for the isolation and characterisation of cholesterol-enriched lipid rafts.

The traditional view of the plasma membrane as a uniform cellular envelope formed from a homogenous mixture of lipids has been refined in recent years to reflect the heterogeneity of its composite lipids. The membrane can consist of upwards of 500 different types of lipids, which exhibit complex and dynamic interactions. Cholesterol and sphingolipids, in particular, partition away from the bulk of bilayer to form distinct microdomains or 'rafts'. Although controversial, lipid rafts have attracted considerable attention over recent years, firstly because of their apparent ability to selectively aggregate interacting signalling molecules, including ion channels and receptors, and secondly because of the implication that they may be involved in the spatial organisation of signalling pathways. Here we describe methods to isolate lipid rafts, assess their purity and determine the distribution of potassium channel proteins between raft and non-raft fractions.