pH-temperature dependence of organic acid transport in rat kidney slices.

Uptake of p-aminohippurate (PAH) by rat kidney slices was optimal at a pH of around 7.3 when incubation temperature was 37 degrees C. At 25 degrees C, however, optimal pH was increased to about 7.5. When the uptake was evaluated as a function of the OH/H ratio of the medium, it was found that optimal uptake is at a constant OH/H. Data showing the same characteristics of OH/H dependence were also observed for phenol red. Passive uptake of PAH was pH independent. Efflux rates for PAH also showed the pH optimal which was identical to that of uptake. At both 25 and 37 degrees C the Km appeared to be independent of pH while the maximum rate of active influx. An optimal OH/H ratio determines maximal velocity and this ratio is fixed and independent of temperature.