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Abstract
Estimation of efflux of amino acids from the mammalian lens indicates it is of small magnitude compared to influx at equivalent nonsaturating levels of substrate. This finding is a necessary part of the explanation of the complex problem of the maintenance of elevated, intracellular levels of these substances. Accelerative countertransport was observed when appropriate amino acids were present on the trans side of the plasma membrane; this phenomenon provides evidence of a mediated path for exodus. The two neutral amino acids examined had rate coefficients for efflux which were similar, and approximately equal to rate coefficients for the nonsaturable component of entry of this category of substrates. On the other hand, the rate coefficient for efflux of L-lysine exceeded that which could be attributed to a nonsaturable process; the difference may be due to lower levels of endogenous, competing diamino acids compared with the neutral amino acids.