Studies on intraocular transport of taurine. II. Accumulation in the rabbit lens.

The accumulation of <C-taurine in the lens was studied by culture technique under a variety of conditions. This compound accumidates in the ocular lens against a concentration gradient by a process lohich can be readily saturated. The saturation mechanism does not conform to Michaelis-Menten kinetics. The transport process is highly dependent upon temperature (Qio = 5), and derives the energy required from anaerobic metabolism of glucose. The accumulation of taurine in the lens is reduced by a number of metabolic inhibitors, and in the absence of calcium, strontium ions may be substituted for calcium. Ouabain significantly decreases the accumidation of taurine, and the effect is from the onset of lens culture suggesting that the amino acid transport is directly linked to the enzyme Na-K-ATPase. Accumulation of taurine is unaffected in a potassium-free medium but is reduced by 50 per cent if potassium ion in the lens is first partially depleted. Decrease in the concentration of sodium ions in the medium also reduces the accumulation of taurine but the lenses could not be maintained in a physiological state so that decreased transport of taurine cannot be ascribed to the specific effect of sodium ion. Transport of taurine is inhibited by a number of structural analogues of this compound. Reciprocal inhibition of 0-alanine transport by taurine was also observed suggesting a common carrier for the two amino acids. Of the various a-amino acids tested, only glycine, alanine, and arginine were found to compete for the taurine transporting system. It is concluded that the high concentration of taurine normally found in the lens is derived, at least in part, by active transport from intraoadar fluids.