Renal tubular reabsorption of cycloleucine (1-amino-cyclopentane carboxylic acid) was studied in vivo et situ by continuous microperfusion of single proximal tubules of the rat. The results show: a) cycloleucine is reabsorbed rapidly compared with other amino acids b) this reabsorption is saturable and can be inhibited by oligomycin c) cycloleucine inhibits tubular reabsorption of L-arginine, glycine, and of L-phenylalanine. Mutual reciprocal inhibition occurs only with L-phenylalanine (and perhaps also with glycine). A maximal possible permeability coefficient for cycloleucine (less than 6 times 10--5 cm times sec--1) was calculated. Assuming simple 2-parameter kinetics, Vmax and Km for tubular reabsorption of cycloleucine were estimated. It can be concluded from the present results that cycloleucine is reabsorbed by a mechanism that transports L-phenylalanine, but not by the system shared by dibasic amino acids.
Absorption Amino Acids