Characteristics of changes in the intracellular potential associated with transport of neutral, dibasic and acidic amino acids in Triturus proximal tubule.
(1)Introduction of L-alanine and L-lysine into the lumen of the proximal tubule of Triturus kidney evoked an immediate and sustained depolarization of the peritubular membrane potential (Epm) and a small increase in the transtubular potential (Ett). L-Aspartate had no effect. (2) The alanine-induced depolarization was absolutely dependent on the presence of Na+, whereas the lysine-induced one was partially dependent on Na+. In the absence of Na+, alanine usually evoked a transient hyperpolarization of the Epm, while lysine evoked a diffusion potential-like PD change. (3) Addition of alanine or lysine to the peritubular fluid did not cause any immediate change in the Epm, but the cells depolarized with a marked time delay. The delayed depolarization could be ascribed to the entrance of amino acids into the lumen through the nephrostromes and the paracellular pathways. (4) Cellular uptake of alanine and lysine was partially dependent on Na+, while that of aspartate was completely dependent on Na+. (5) Characteristics of the observed electrical events were explained in terms of the differences in the charge transfer associated with transport of these amino acids across the luminal membrane.