Interaction of colchicine with phosphatidylcholine membranes

Abstract

EXPERIMENTAL results have suggested that the alkaloid drug colchicine affects the lateral mobility of membrane components^1–5. To explain these observations, Wunderlich et al.⁶ have proposed two alternative hypotheses: the lipophilic drug intercalates into the lipid bilayer in a manner analogous to cholesterol; or colchicine acts by binding to membrane protein. It is well documented that in lipid bilayers of both model and biological membranes, the methylene groups of the lipid fatty acyl chains are more mobile near the chain terminus than near the glycerol backbone of the phospho-lipid, resulting in a gradient of increasing fluidity in the non-polar phase of the bilayer interior^7–12. From nuclear magnetic resonance (NMR) and spin-label electron spin resonance (ESR) studies it has been found that cholesterol, by intercalating between the phospholipid fatty acyl chain, markedly increases the rigidity of the hydrocarbon phase of the bilayer^13–19. We present here the results of a detailed spin-label study using phosphatidylcholine (PC) liposomes to show that, in contrast with cholesterol, colchicine does not detectably change the rigidity of PC bilayers.