Effect of isoflurane on multilamellar liposome-Analysis by 19F-NMR

[Objectives] To investigate the interaction of a general anesthetic with biological membranes, we measured 19F nuclear magnetic resonance (NMR) spectra of isoflurane on the isoflurane-multilamellar liposome (MLV) system. The paramagnetic effect of the spin-probe was examined to obtain the spatial structure between isoflurane and spin-probe in the MLV. [Methods] We made the MLV solution including spin probe, 5- or 16-doxyl stearic acid (5- or16-DSA), added isoflurane to the MLV solution and obtained chemical shifts, the spin-lattice relaxation time (T1) and the spin-spin relaxation time (T2) of isoflurane on the spectra at 7T. [Results and Discussion] The addition of isoflurane did not change the chemical shifts and the T1, but line widths became slightly broad and the T2 decreased remarkably, suggesting that isoflurane affects a chemical-exchange process between free and bound isoflurane on MLV. T1 and the T2 furthermore decreased in the presence of 5-DSA or 16-DSA due to the paramagnetic interaction between 19F nuclei of isoflurane and the electron of the spin-probe. T1 and T2 with 5-DSA were shorter than those of 16-DSA. These results suggest that the di stance between isoflurane and 5-DSA in MLV is closer than that of 16-DSA, and that isoflurane molecules locate in the outer surface of MLV