To the Editor:-We recently realized that the concentrations of volatile anesthetics reported in our publications [1,2]are incorrect. It follows that the activity of the plasma membrane Calcium sup 2+ -ATPase (PMCA) is half-maximally inhibited (I50values) at 2.2-3.0 mM (instead of 0.22-0.30 mM) halothane and 2.4-3.2 mM (instead of 0.24-0.32 mM) isoflurane, which compare to 7.5-12 minimum alveolar anesthetic concentrations.
Although we cannot claim that PMCA is inhibited by volatile anesthetics at their clinical concentrations, all other findings presented in our papers are unaffected by the concentration error. These are: 1) analogous dose-dependent inhibition of PMCA activity by volatile anesthetics in neuronal and red cell membranes; 2) significantly higher sensitivity of the PMCA as compared with three other plasma membrane ATPases to the inhibitory action of halothane and isoflurane; and 3) lack of difference in sensitivity of PMCA versus the other ATPases to sodium pentobarbital, which inhibits them at 100- to 200-fold above its anesthetic concentrations.
With these in mind, we use the PMCA as a model of a membrane protein on which molecular events of anesthetic action could be elucidated.
Danuta Kosk-Kosicka, Ph.D., Associate Professor, Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, 600 North Wolfe Street/Blalock 1404-C, Baltimore, Maryland 21287-4961.
(Accepted for publication August 14, 1996.)