Effects of Halothane, Enflurane, and Isoflurane on Measurements of Ca2+ by Calcium Electrode and Aequorin Luminescence

Abstract

We assessed the possible effects of the volatile halogenated anesthetics halothane, enflurane, and isoflurane on Ca2+ electrode measurements and on the Ca2+ sensitivity of the bioluminescent protein aequorin. In Ca2+–EGTA buffers of different pCa values (7.870, 6.726, 6.033, 4.974, 4.038, and 2.995) and in serial Ca2+ dilutions (10−4, 10−3, and 10−2 M), halothane, enflurane, and isoflurane each caused a concentration-dependent and reversible increase in the absolute value of the negative electrode potential. Isoflurane and enflurane had larger effects than halothane. Neither of these anesthetics changed aequorin luminescence at any pCa tested in the range 2–8. There was no potentiation or inactivation of aequorin luminescence over a period of up to 2 h. These results suggest that (1) halothane, enflurane, and isoflurane interfere with Ca2+ electrode measurements, most likely by changing the physicochemical properties of the membrane; (2) these anesthetics do not inactivate or otherwise modify the characteristics of the reaction of Ca2+ with aequorin; and (3) these anesthetics do not change the apparent affinity of EGTA for Ca2+.