Volatile General Anesthetic Interactions with a Bacterial Sodium Channel

Abstract

General anesthesia results from complex interactions involving ion channels in the brain. Voltage-gated ion channels are modulated by halogenated inhaled general anesthetics, however the drug-channel interactions are generally believed to be non-specific making it difficult to investigate the molecular mechanisms of anesthetic action. We find, however, that the bacterial sodium channel NaChBac exhibits differential regulation by different general anesthetics, suggesting that there may be specific interactions. Molecular dynamics (MD) simulations have identified several possible binding sites for isoflurane in the NaChBac channel structure. Here, we have characterized the affinity, occupancy and hydrogen bonding for these sites and identified key interactions. In addition, experimental evidence suggests that both isoflurane and sevoflurane have dual actions on NaChBac, possibly involving action at two different sites. Consistent with pore block, sevoflurane accelerates the decay of the current (20% faster at 0.4 mM sevoflurane) but, at the same time, increases the peak current (10% increase with 0.4 mM sevoflurane), which argues against the blocking mechanism. We hypothesize that an additional mechanism involving a distinct site is necessary to explain the latter effect. We are currently employing MD simulation and structural modeling combined with mutagenesis and electrophysiology to test this two-site hypothesis and investigate the molecular mechanisms of these opposing effects. Supported by NINDS F31 NS077689 (AFB) and NIGMS P01 GM0558 (MLK).