Mechanisms of Voltage-Gated Na+ Channel Inhibition by Propofol
Propofol is one of the most widely used intravenous general anesthetics. As with most general anesthetics, however, our understanding of its mechanism of action remains incomplete, and in the broader sense, it is not known how a chemically diverse group of compounds elicits the same clinical endpoints of anesthesia. A growing body of work points to ion channels of the nervous system as an important class of anesthetic targets that may be responsible for not only desired endpoints but also adverse effects. In particular, voltage-gated Na+ channels (Navs), which are critical for excitability in the nervous system, have been implicated in the mechanism of general anesthesia. Understanding the role of Navs in general anesthesia and the mechanisms that govern anesthetic-Nav interactions would be a significant step toward targeted drug design and improved clinical use of these essential but potentially toxic agents. The work presented here used a combination of electrophysiology, mutagenesis, kinetic modeling, molecular dynamics, and photoaffinity labeling to investigate the biophysical and molecular mechanisms that underlie propofol modulation of Navs. Investigating NaChBac and NavMs, two anesthetic-sensitive prokaryotic homologs of eukaryotic Navs, we determined that propofol does not inhibit Navs by slow or fast pore block. Instead, we found that propofol is primarily a positive gating modulator of NaChBac and NavMs and ultimately inhibits them by promoting activation-coupled inactivation. Molecular dynamics simulations and molecular docking uncovered potential propofol interactions with the gating machinery that could underlie the observed effects. In an independent approach, we used photoaffinity labeling to more directly identify residues and binding sites involved in propofol binding to NaChBac and NavMs. Remarkably, these experiments also revealed interaction/binding sites in the gating machinery. Deeper investigation of these sites with mutagenesis indicated that the binding pocket near the S4-S5 linker could be responsible for the modulation of Nav inactivation gating by propofol, a finding that appears to be conserved among other six-transmembrane ion channels. The work presented here broadens our understanding of Nav inhibition by propofol and presents new opportunities to investigate the structural basis of this mechanism of action.
Yang, Elaine, "Mechanisms of Voltage-Gated Na+ Channel Inhibition by Propofol" (2020). ETD Collection for Thomas Jefferson University. AAI27740110.