Accumulation of taurine by cultured retinal pigment epithelium of the rat.

Cultured rat retinal pigment epithelium actively accumulates taurine against a concentration gradient; an intracellular concentration of 12 mM is maintained at an extracellular taurine concentration of 0.12 mM. Taurine accumulation conforms to Michaelis-Menten kinetics for extracellular taurine concentrations between 0.006 and 0.05 mM; within that range the Km is 16 muM and the Vmax is 2.3 nmol./hr./mul of cells. Above an extracellular concentration of 0.5 mM the kinetics are complex. Accumulation is inhibited by reduced temperature and iodoacetate as well as by dinitrophenol in the absence of glucose. Ouabain, reduced extracellular sodium, and removal of extracellular potassium and calcium also inhibit taurine accumulation. The cells also release previously accumulated taurine at half-time of 1 to 3 hours. The rapid accumulation and release of taurine by cultured retinal pigment epithelial cells is consistent with the idea that this tissue is a site for the transport of taurine in vivo.