Journal
BRITISH JOURNAL OF PHARMACOLOGY
Volume 159, Issue 4, Pages 872-878Publisher
WILEY
DOI: 10.1111/j.1476-5381.2009.00583.x
Keywords
inhaled anaesthetics; isoflurane; MAC; mechanisms of anaesthetic action; sodium channels; tetrodotoxin; veratridine
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Funding
- NIH [1P01GM47818, GM58055]
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Background and purpose: Results from several studies point to voltage-gated Na+ channels as potential mediators of the immobility produced by inhaled anaesthetics. We hypothesized that the intrathecal administration of tetrodotoxin, a drug that blocks Na+ channels, should enhance anaesthetic potency, and that concurrent administration of veratridine, a drug that augments Na+ channel opening, should reverse the increase in potency. Experimental approach: We measured the change in isoflurane potency for reducing movement in response to a painful stimulus as defined by MAC (minimum alveolar concentration of anaesthetic required to abolish movement in 50% of subjects) caused by intrathecal infusion of various concentrations of tetrodotoxin into the lumbothoracic subarachnoid space of rats, and the change in MAC caused by the administration of a fixed dose of tetrodotoxin plus various doses of intrathecal veratridine. Key results: Intrathecal infusion of tetrodotoxin (0.078-0.63 mu M) produced a reversible dose-related decrease in MAC, of more than 50% at the highest concentration. Intrathecal co-administration of veratridine (1.6-6.4 mu M) reversed this decrease in a dose-related manner, with nearly complete reversal at the highest veratridine dose tested. Conclusions and implications: Intrathecal administration of tetrodotoxin increases isoflurane potency (decreases isoflurane MAC), and intrathecal administration of veratridine counteracts this effect in vivo. These findings are consistent with a role for voltage-gated Na+ channel blockade in the immobility produced by inhaled anaesthetics.
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