The effects of medium pH and temperature on glutamine uptake, NH3 production and CO2 production were examined using kidney cortex slices from normal and acidotic rats. 2. Uptake of glutamine by kidney slices from normal rats shows a pH optimum of 7.5 at 25 degrees C and 7.3 at 37 degrees C. Uptake is optimal, however, at a constant OH-/H+ ratio of 10. 3. In slices from acidotic rats greatest uptake was at pH 6.8 at 25 degrees C and 6.6 at 37 degrees C. Optimal OH-/H+ ratio was 0.4 and constant at both temperatures. 4. CO2 production from glutamine was greatest at pH 7.0 at 37 degrees C in slices from control rats. No pH optimum was detected at 25 degrees C. With slices from acidotic animals, optimal pH for CO2 production became identical with that for uptake. 5. Both basal and glutamine-stimulated NH3 production showed no optimal pH but were significantly higher in slices from acidotic rats compared with those from controls. 6. Dependence of glutamine penetration on optimal OH-/H+ ratio is considered to reflect a general membrane phenomenon which is produced by either an increase in carrier-substrate complexes or an increase in the number of carriers at this ratio. 7. Cellular penetration of glutamine does not appear to be a limiting factor in production of NH3 in vitro.
