alpha/Amino/n/butyric acid methyl ester induces concentrative uptake of L/dopa in human Langerhans' cells normally not operative for L/dopa transport.

Abstract

We recently reported the existence of two kinds of human epidermal Langerhans' cells (LC), one which can take up and accumulate L/dopa and one which cannot. The dopa(+) LC take up L/dopa by carrier/mediated exchange diffusion, that is, the influx of L/dopa and the outflow of an intracellular substance are linked via the same carrier. The nature of the fundamental difference between L/dopa(+) and L/dopa(/) cells has not been clarified. We have now found that alpha/amino/n/butyric acid methyl ester (ABA/OME) penetrates into intracellular compartments, perhaps endosomes or lysosomes, of all LC, where hydrolysis results in the accumulation of the free amino acid (ABA). This accumulation causes a considerable increase in osmotic pressure of the membrane/limited organelle, leading to influx of water and swelling. Co/incubation with L/dopa revealed an influx of L/dopa into LC which normally cannot take up this amino acid. It is suggested that these LC lack the capacity to synthesize and/or store the counterpart which allows L/dopa to enter the dopa(+) LC, but that ABA in the L/dopa(/) LC can function as an equivalent counterpart.