Carbon dioxide negatively modulates N-methyl-d-aspartate receptors

Robert J Brosnan, T. L. Pham

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Background. Carbon dioxide (CO2) dose-dependently decreases minimum alveolar concentration (MAC) of anaesthetics in rats. CO2 also dose-dependently decreases cerebrospinal fluid pH. N-methyl-d-aspartate (NMDA) channels exhibit pH sensitivity and are putative targets for inhaled anaesthetics. We hypothesized that CO2 dose-dependently decreases rat NMDA channel current via an acidifying effect at concentrations relevant to CO2 MAC. Methods. To test this hypothesis, we studied rat NR1/NR2A glutamate receptors expressed in voltage-clamped Xenopus oocytes. To measure pH effects, we used perfusates adjusted between 7.3 and 5.3 with HCl. To measure CO2 effects, we used equimolar sodium perfusates containing either 0 or 24 mM NaHCO3 and CO2 between 0% and 87% atm. Solution compositions were measured using a blood gas analyser with values corrected using a calibrated pH meter and gas chromatograph with solutions at 37°C. Results. We found that decreasing pH decreased NMDA current. Moreover, pH effects produced by adding CO2 to NaHCO3-containing perfusates were identical to those produced by adding HCl to normal perfusates. The pH inhibiting 50% of NMDA current was 6.52. The CO2 concentration inhibiting 50% of rat NMDA current was 63% for solutions with 24 mM NaHCO 3. CO2 exhibited a linear dose-dependent NMDA response analogous to that observed for in vivo CO2 anaesthetic potency in rats. Conclusions. CO2 and hydrogen ions act via the same mechanism to inhibit NMDA receptors. Moreover, CO2 inhibits rat NMDA receptors in a manner that is consistent with CO2 MAC-sparing effects in rats.

Original languageEnglish (US)
Pages (from-to)673-679
Number of pages7
JournalBritish Journal of Anaesthesia
Volume101
Issue number5
DOIs
StatePublished - Nov 2008

Keywords

  • Anaesthesia
  • Anaesthetic gases
  • Carbon dioxide
  • Hypercapnia
  • Ion channels
  • N-methyl-D-aspartate
  • pH
  • Receptor pharmacology

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

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