New mechanism for amino acid influx into human epidermal Langerhans cells: L-dopa/proton counter-transport system.
We have characterized a stereospecific transport mechanism for L-dopa into human epidermal Langerhans cells (LCs). It is different from any other amino acid transport system. It is highly concentrative, largely pH-independent, and independent of exogenous Na+, glucose and oxygen, and fuelled by a renewable intracellular energy source inhibited by iodoacetate but not by arsenate. We propose that the mechanism is a unidirectional L-dopa/proton counter-transport system. We have recently demonstrated anaerobic glycolysis in human epidermis, which substantiates the need of proton pumps for resident LCs. The findings prompt a re-evaluation of the profound changes LCs undergo when exposed to oxygen in aerobic culture. L-dopa is not metabolized by LCs but can rapidly be dislocated to the intercellular space by certain extracellular amino acids, i.e. LCs can profit by L-dopa in a dualistic way, altogether a remarkable biological phenomenon.
Falck
Bengt
B
Department of Physiology, Lund University, Lund, Sweden.
Bendsoe
Niels
N
Ronquist
Gunnar
G
D000328:Adult; D000596:Amino Acids / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology; D015259:Dopamine Agents / Q000493:pharmacokinetics*; D004734:Energy Metabolism / Q000502:physiology; D000078404:Epidermal Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007801:Langerhans Cells / Q000378:metabolism*; D007980:Levodopa / Q000493:pharmacokinetics*; D011522:Protons; D012964:Sodium / Q000378:metabolism; D013696:Temperature
D000596:Amino Acids; D015259:Dopamine Agents; D011522:Protons; D007980:Levodopa; D012964:Sodium