Figure 7. Effect of discontinuing in vitro halothane exposure on PMCA pump activity. Calcium²+ transport was measured in cerebral SPM from previously unexposed rats, as described in the text. The vertical axis indicates Calcium²+ uptake (nmoles *symbol* mg protein sup -1) and the horizontal axis denotes incubation time in minutes and halothane concentration (mM) in treated incubation mixtures at 30, 60, and 90 min. Treated vials (open circles or triangles) were exposed to 1.5% halothane, delivered as described in the text, for 30 min, followed by air/oxygen for the remainder of the incubation period. Control vials (solid circles or triangles) were exposed to air/oxygen only; ATP was added at t = 0 (circles) or at t = 30 min (triangles). Aliquots were obtained at 30, 60, and 90 min for assay of Calcium²+ uptake and for measurement of halothane concentration. Indicated values represent the mean of triplicate measurements on SPM pooled from ten rats in two experiments. Error bars indicate 95% confidence limits from ANOVA. Halothane reduced Calcium²+ uptake to 81% of control when ATP was added before halothane exposure and to 85% of control when ATP was added after halothane was discontinued (P < 0.01).