The effect of isoflurane on erythrocyte membranes studied by ATR-FTIR

The effect of isoflurane on erythrocyte membranes has been investigated by means of attenuated total reflection infrared spectroscopy. Infrared spectra were measured on sonicated erythrocyte ghosts layered upon a ZnSe crystal covered with D(2)O saline solutions containing increasing amounts of isoflurane. At clinically relevant anesthetic concentrations and 37 degrees C, significant changes in the structural and dynamic properties of the membrane phospholipid bilayers are observed. Both the acyl chain methylene symmetric and asymmetric stretching modes and the carbonyl ester stretching band displayed frequency shifts interpreted as transitions toward disordered liquid-like structure accompanied by dehydration of the phospholipid polar heads. In turn, no secondary structure-linked changes are observed in the amide I region of membrane proteins. Higher anesthetic concentrations (500-900 microM), resulted in progressive detachment of the multilayers from the ATR crystal and irreversible formation of denatured protein. Polarization studies in correspondence of the acyl lipid methylene stretching bands indicated that isoflurane decreases the dichroic ratio thus inducing disorder in the orientation of the lipid acyl chains.