Optical Reversal of Halothane-Induced Immobility in C. elegans

Abstract

Summary Volatile anesthetics (VAs) cause profound neurological effects, including reversible loss of consciousness and immobility. Despite their widespread use, the mechanism of action of VAs remains one of the unsolved puzzles of neuroscience [1,2]. Genetic studies in C. elegans [3, 4], Drosophila [3,5], and mice [6–9] indicate that ion channels controlling the neuronal resting membrane potential (RMP) also control anesthetic sensitivity. Leak channels selective for K+ [10–13] or permeable to Na+ [14], are critical for establishing RMP. We hypothesized that halothane, a VA, caused immobility by altering the neuronal RMP. In C. elegans, halothane induced immobility is acutely and completely reversed by channelrhodopsin-2 based depolarization of the RMP when expressed specifically in cholinergic neurons. Furthermore, hyperpolarizing cholinergic neurons via halorhodopsin activation increases sensitivity to halothane. The sensitivity of C. elegans to halothane can be altered by 25-fold by either manipulation of membrane conductance with optogenetic methods or generation of mutations in leak channels that set the RMP. Immobility induced by another VA, isoflurane, is not affected by these treatments, thereby excluding the possibility of non-specific hyperactivity. The sum of our data indicates that leak channels and the RMP are important determinants of halothane-induced general anesthesia.

Novel Activation of Voltage-gated K+ Channels by Sevoflurane

“…Concluding Remarks and Implications-Toward understanding the molecular mechanisms of general anesthesia, recent reports emphasized the need to investigate how halogenated inhaled anesthetics with very similar chemical properties can achieve functional specificity (34,41). This study offers insight into this problem by suggesting that allosteric interactions affecting activation gating of Kv channels can explain the novel positive allosteric modulation of an archetypical Kv channel by the inhaled anesthetic sevoflurane.…”

Genetic and Anatomical Basis of the Barrier Separating Wakefulness and Anesthetic-Induced Unresponsiveness

“…Interestingly, of the mutations that been shown to affect general anesthesia, those with the biggest impact in flies (our data) and mammals [42] cause impairment of ion channel function. Whether these effects are due to loss of drug binding sites in the proteins affected by these mutations, or whether the resulting changes in membrane potential alter anesthetic efficacy [43] remains to be determined. Pharmacokinetics do not appear to be a factor, however, since at the EC 50 for emergence in both flies and mammals, isoflurane concentrations are similar in controls and mutants that have altered neural inertia [7].…”

NALCN Ion Channels Have Alternative Selectivity Filters Resembling Calcium Channels or Sodium Channels

“…A reliable consequence of NALCN knockdown is a membrane hyperpolarization [4], [11], [37]. Invertebrates have increased sensitivity to volatile anesthetics [38], [39] and defects in exocytosis [[7]–[10], that could relate to NALCN's influence on membrane potential serving to regulate secretion in neurons that require fast or continuous vesicle turnover.…”