Studies on the kinetics of gramicidin channels in liposomes: Part I

Abstract

Sonicated phospholipid vesicles (liposomes) with an entrapped fluorescent dye (pyranine) have been used as a model system to study the kinetics of a channel forming ionophore, gramicidin. The addition of gramicidin to the liposomes in the presence of a pH gradient leads to a rapid decrease in the fluorescence of the entrapped pH sensitive fluorescent probe, from which initial slopes were measured manually and the kinetics of incorporation were calculated. A similar experiment was carried out with liposomes containing 25 mol% cholesterol to determine the influence of cholesterol on gramicidin channel incorporation rates. In case of low concentrations of gramicidin (100-1000 nM), the initial rates are far above theoretical expectation and do not follow the Poisson distribution.