Experimental schematic of calcium release detection and RyR1 activation by isoflurane (A) Schematic diagram of the experimental system that detects calcium release from the endoplasmic reticulum by each ryanodine receptor. (B) Isoflurane selectively activates RyR1. Credit: PLOS Biology (2025). DOI: 10.1371/journal.pbio.3003172
Since their effects were discovered approximately 180 years ago, inhalational anesthetics have been used for general anesthesia in surgical operations. However, the mechanism of their anesthetic effect has not yet been fully revealed. Previous studies have shown that inhalational anesthetics exert their anesthetic effects by acting on multiple proteins, but the presence of unknown target molecules has also been suggested.
In rare cases, patients with abnormal type 1 ryanodine receptors (RyR1) (RyR1 mutations) have been known to be at higher risk of malignant hyperthermia, which can be caused by inhalational anesthetics. However, the direct molecular interaction between inhalational anesthetics and RyR1 has not been clearly demonstrated, and the relationship between RyR1 and anesthetic effects has also been unknown.
In a new study in PLOS Biology, a research group led by Professor Hiroki Ueda of the Graduate School of Medicine, The University of Tokyo, found that RyR1 which is a calcium release channel, induces general anesthesia by serving as a target molecule of inhalational anesthetics.
The research group first confirmed that isoflurane and other inhalational anesthetics activate RyR1 and stimulate calcium release from the endoplasmic reticulum. The amino acid residues in RyR1, which play an important role in the isoflurane-induced activation, were identified, and the binding site of isoflurane was estimated.
Additionally, the research group created a genetically modified mouse (knock-in mouse) which expressed the RyR1 mutant that does not respond to isoflurane. When the knock-in mice were exposed to isoflurane, they demonstrated a partially reduced sensitivity to anesthesia compared to normal mice.
Identification of key amino acid residues and new compounds targeting the putative isoflurane binding site (A) Isoflurane response of RyR1 mutant in which the 4000th amino acid (methionine, M) was replaced with phenylalanine (F). Compared to the wild type (WT, normal RyR1 without mutation), the isoflurane response is reduced. (B) Loss of righting reflex of knock-in mice expressing RyR1 mutants with reduced isoflurane response. The knock-in mice were partially less susceptible to anesthesia compared to WT mice (normal mice). Hetero: mice in which only one allele is mutated. Homo: mice in which both alleles are mutated. (C) Loss of righting reflex of mice treated with a novel compound targeting the putative isoflurane binding site. The sensitivity to isoflurane was increased. Note that saline has no physiological activity. Credit: PLOS Biology (2025). DOI: 10.1371/journal.pbio.3003172
Furthermore, new compounds that target the putative binding site of isoflurane were identified from in silico compound screening and were found to have sedative-like effects in mice. These results suggest that RyR1 is a functional target of isoflurane that is directly related to its anesthetic properties.
This research reveals one aspect of the molecular mechanism of inhalational anesthetics used for general anesthesia. This is a new finding as previous studies have not demonstrated the relationship between RyR1 and anesthetic effects in mammals. A more detailed understanding of anesthetics' mechanism of action could lead to the development of better anesthetics and treatment methods.
More information: Hiroyuki J. Kanaya et al, Isoflurane activates the type 1 ryanodine receptor to induce anesthesia in mice, PLOS Biology (2025).
Journal information: PLoS Biology
Provided by Japan Science and Technology Agency (JST)
