alpha-Amino-n-butyric acid methyl ester induces concentrative uptake of L-dopa in human Langerhans' cells normally not operative for L-dopa transport.
Falck B, Andersson L, Mikulowska A, Ronquist G.
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.