Figure 3. Inhibition by xenon and nitrous oxide (1.3 MAC equivalents) of Calcium²+-ATPase pump activity in synaptic plasma membranes from rat brain. Minimum alveolar concentration was taken as 0.95 atmospheres for xenon [22] and 1.54 atmospheres for nitrous oxide. [23] Total pressure in the incubation chamber for both treatment groups was 1.5 atmospheres for xenon and 2.5 atmospheres for nitrous oxide. Open columns represent Calcium²+-ATPase pump activity in membranes exposed to helium alone, and hatched columns indicate activity in membranes exposed to a mixture of helium and xenon (A) or nitrous oxide (B). (A) The effect of xenon on membranes from four different brain regions: cerebrum, cerebellum, midbrain, and medulla. Mean values for all brain regions (total) are shown on the right of the figure. Values shown for each brain region are means from five separate experiments, each carried out with membranes pooled from 12 rats. Error bars indicate 95% confidence limits. An asterisk indicates significant differences between treatment groups for each brain region (P < 0.05), as determined by ANOVA. (B) The effect of nitrous oxide on membranes from rat cerebrum. Values represent the mean of six separate experiments. Nitrous oxide depressed Calcium²+ uptake significantly (P < 0.01).