Sterol specific inactivation of gramicidin A induced membrane cation permeability

Channel inactivation, a time-dependent decrease of the high-cationic permeability induced by gramicidin A, has been found both in cholesterol containing red blood cell membranes and lipid bilayers (Schagina et al., (1989) Biochim. Biophys. Acta 978, 145-150). The rate of channel inactivation strongly depends on the phospholipid to cholesterol molar ratio of the membrane. The channel inactivation is suggested to be the result of an interaction between gramicidin and cholesterol in a stoichiometry of 1:5. Cholesterol dependent inactivation is shown also for gramicidin A analogs: tryptophan-N-formylated gramicidin A, o-pyromellitilgramicidin and malonylbisdesformylgramicidin. When cholesterol in the membrane is substituted by sitosterol, the inactivation of gramicidin-induced cation permeability is preserved, while in the presence of either ergosterol or 7-dehydrocholesterol no indication of the channel inactivation is observed. Thus, the structure of the 'B', ring, not the apolar tail of the sterol molecule, appears to be important in the inactivation process.