Electrophysiological study of L-lysine transport across Triturus proximal tubule: evidence for Na(+)-independent entry and Na(+)-dependent exit.
Cell membrane depolarization induced by intraluminal injection of lysine was entirely independent of the presence of Na+ in Triturus proximal tubule, confirming our previous observation. The amplitude of the depolarization conformed to Michaelis-Menten kinetics regardless of the presence or absence of Na+ in the perfusion solutions. pH of the intraluminal solution had no effect on the electrical response in its range from 5.5 to 8.5. In a Na(+)-free medium, particularly in a Tris-substituted medium, the depolarization induced by a constant concentration of lysine gradually decreased in its size when injection followed by washout of lysine was repetitively tested. The addition of Na+ to the peritubular side after extinction of the responsiveness resulted in a significant restoration of the voltage response to intraluminal lysine. In addition, influx of Na+ from the peritubular fluid into the cells was significantly greater in lysine-loaded tubules than in nonloaded tubules as indicated by a greater rate of increase in intracellular Na+ activity in the presence of ouabain. The data strongly suggest that lysine enters the cells via an electrogenic uniport mechanism and leaves the cells via Na+:amino acid exchange transport mechanism.
Laboratory of Physiology, School of Food and Nutritional Sciences, University of Shizuoka, Japan.
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Nunokawa
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Hoshi
D000818:Animals; D001693:Biological Transport, Active; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D012964:Sodium / Q000378:metabolism*; D014319:Triturus / Q000378:metabolism
D012964:Sodium; D008239:Lysine