ALPHA-AMINO-N-BUTYRIC ACID METHYL-ESTER INDUCES CONCENTRATIVE UPTAKE OF L-DOPA IN HUMAN LANGERHANS CELLS NORMALLY NOT OPERATIVE FOR L-DOPA TRANSPORT

We recently reported the existence of two kinds of human epidermal Lan gerhans' cells (LC), one which can take up and accumulate 1-dopa and o ne which cannot. The dopa(+) LC take up I-dopa by carrier-mediated exc hange diffusion, that is, the influx of 1-dopa and the outflow of an i ntracellular substance are linked via the same carrier. The nature of the fundamental difference between L-dopa(+) and L-dopa(-) cells has n ot been clarified. We have now found that alpha-amino-n-butyric acid m ethyl ester (ABA-OME) penetrates into intracellular compartments, perh aps 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 org anelle, leading to influx of water and swelling. Co-incubation with L- dopa revealed an influx of 1-dopa into LC which normally cannot take u p this amino acid. It is suggested that these LC lack the capacity to synthesize and/or store the counterpart which allows 1-dopa to enter t he dopa(+) LC, but that ABA in the L-dopa(-) LC can function as an equ ivalent counterpart.