ENZYMATIC FACTORS IN RENAL TUBULAR SECRETION OF PHENOL RED

Abstract

The enzymatic factors involved in the secretion of phenol red into the lumen of the proximal tubules of mammalian kidney slices were studied. The optimal pH value was 7.8. Phenol red was used in a concn. of 1.06 x 10-4 [image] (4 mg./100 cc). Slices of renal cortex from frogs, rabbits, rats, mice and guinea pigs may be used to demonstrate the active secretion of phenol red in vitro. Compounds which inhibit the activity of dehydrogenases, oxidases, phosphorylases, transphosphorylases or cytochrome will inhibit the secretion in a non-specific manner. Therefore, the maintenance of a coupled oxidation/phosphorylation system is essential in that it functions as a source of the energy required for the active transport of phenol red. Carinamide acts as a specific, reversible inhibitor at a concn. of 5 x 10-4 [image] without inhibiting oxygen uptake. The latter compound apparently is not a non-specific inhibitor of energy-rich phosphate formation or utilization, for it is of a low order of toxicity, does not inhibit the renal elimination of N-methylnicotinamide, nor is there any relationship between the activities of individual compounds of a series of carinamide homologs with respect to (a) inhibition of phenol red secretion and (b) systemic toxicity. Apparently carinamide inhibits some definitive component of the system involved in the transport of phenol red by the cells of the proximal tubules of mammalian kidney, since it is not an inhibitor of renal secretory processes in general.