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Abstract
Rabbit ciliary body-iris preparations accumulate 14C-fluorescein against a concentration gradient when incubated in Tyrode's solution at 37 degrees C and pH 7.4 for 1 hr. Under these conditions, fluorescein metabolism is negligible. This accumulation is depressed by cyanide, dinitrophenol, iodoacetate, by incubation in glucose-free medium, and by incubation at 0 degrees C. This uptake is not inhibited significantly by incubation in sodium-free medium, and relatively high concentrations of ouabain are necessary to cause inhibition. Initial uptake studies show saturation kinetics with half-saturation concentration = 0.12 mM and maximum accumulation rate = 2.3 mmoles/hr/kg wet tissue weight. Fluorescein thus appears to accumulate by a carrier-mediated active uptake process. On the basis of series of competition experiments, it is concluded that fluorescein uptake and p-aminohippurate uptake occur by similar, although not identical, mechanisms.