Anesthetic and non-anesthetic effects on interfacial lipids around an ion channel

All atom molecular dynamics simulations were used to investigate the anesthetic and non-anesthetic effects on the dynamics of bulk and the interfacial dimyristoylphosphatidylcholine lipids surrounding a gramicidin-A (gA) channel. Two pairs of simulations in the presence and absence of halothane and of hexafluoroethane (HFE) were carried out for 2.2 and 8 ns, respectively. The order parameters, determined from the asymptotes of the autocorrelations of the vector between the nitrogen and the immediate methylene carbon of the choline head group and the Ci−1 - Ci+1 vectors for the ith carbon (Ci) in the lipid chains, show that the head groups are less ordered in the interfacial lipids than in the bulk lipids, and that neither halothane nor HFE at 5 mol% concentration has significant effects on the ordering of the interfacial or bulk lipid chains. Because halothane and HFE produce distinctly different effects on the global dynamics of gA channel, it is unlikely that anesthetic effects on gA are indirectly mediated through the lipids.