ACTIVE ACCUMULATION OF ¹⁴C-SALICYLIC ACID BY RAT KIDNEY CORTEX IN VITRO

¹ Department of Pharmacology, Medical College of Virginia, Health Sciences Division, Virginia Commonwealth University, Richmond, Virginia

Uptake of salicylic-7-¹⁴C acid by rat kidney cortex slices was measured under varied incubation conditions. The slice/medium concentration ratio (counts per minute per gram divided by counts per minute per milliliter) reached a steady-state value of 4.7ml/g in one hour. Uptake of ¹⁴C-salicylate was significantly decreased by each of the following: 1) N₂ atmosphere, 2) 5°C, 3) preheating for 10 minutes at 60°C, 4) NaN₃ (5 mM). Uptake was also significantly inhibited by a number of structurally similar organic acids. Although efflux was enhanced by externally applied salicylic acid or benzoic acid, the increase was probably due to inhibition of an unavoidable back flux occurring during efflux. When anaerobic uptake was subtracted, uptake followed Michaelis-Menten kinetics with a V_max of 0.31 µmol/ml-min and a K_m of 0.155 mM. Thus, uptake of ¹⁴C-salicylate by rat kidney cortex slices appears to meet the criteria for an active transport system with simultaneous passive diffusion.

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