R (+) etomidate and the photoactivable R (+) azietomidate have comparable anesthetic activity in wild-type mice and comparably decreased activity in mice with a N265M point mutation in the gamma-aminobutyric acid receptor beta3 subunit.

A photoactivable diazirine derivative of etomidate, azietomidate, shares many actions of etomidate, including a capacity to abolish the righting reflexes in tadpoles and enhance gamma-aminobutyric acid (GABA)-induced currents. Azietomidate's usefulness in studies of mechanisms of anesthesia depends on the assumption that it shares a site of action with etomidate. Mice bearing an N265M beta3 subunit point mutation in GABA(A) receptors have a markedly decreased sensitivity to loss of righting reflexes induced by etomidate over a range of doses. Accordingly, in the present study we measured the time to recovery of righting reflexes of wild type and mutant mice as a function of dose given as an IV bolus. Analysis of the data for azietomidate yielded mean times to recovery of righting reflexes at a dose of 7.5 mg/kg of 10.0 +/- 0.9 min and 3.0 +/- 1.6 min for wild type and mutant mice, respectively (mean +/- sd). A similar analysis for etomidate yielded mean times to recovery of righting reflexes at a dose of 7.5 mg/kg of 12.0 +/- 1.3 min and 4.0 +/- 0.7 min for wild type and mutant mice respectively. Thus, at this dose a single mutation, N265M on the beta3 subunit of the GABA(A) receptor, approximately halved the time to recovery of righting reflexes for both etomidate and azietomidate (by 7.6 +/- 1.5 min and 7.2 +/- 1.8 min, respectively), emphasizing the contribution of this residue as a determinant of a behavioral response of azietomidate in mice.