Effects of halothane, enflurane, and isoflurane on measurements of Ca2+ bycalcium electrode and aequorin luminescence

We assessed the possible effects of the volatile halogenated anesthetics ha lothane, enflurane, and isoflurane on Ca2+ electrode measurements and on th e Ca2+ sensitivity of the bioluminescent protein aequorin. In Ca2+-EGTA buf fers 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, en flurane, and isoflurane each caused a concentration-dependent and reversibl e increase in the absolute value of the negative electrode potential. Isofl urane and enflurane had larger effects than halothane. Neither of these ane sthetics changed aequorin luminescence at any pCa tested in the range 2-8. There was no potentiation or inactivation of aequorin luminescence over a p eriod of up to 2 h. These results suggest that (1) halothane, enflurane, an d isoflurane interfere with Ca2+ electrode measurements, most likely by cha nging 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+. (C) 2000 Academic Press.