Dipeptide-induced Cl- secretion in proximal tubule cells

During a survey of dipeptides that might be transported by therenal PEPT2 transporter in proximal tubule cells, we discovered thatacidic dipeptides could stimulate transient secretory anion current andconductance increases in intact cell monolayers. The stimulatory effectof acidic dipeptides was observed in several proximal tubule cell linesthat have been recently developed by immortalization of early proximaltubule primary cultures from the Wistar-Kyoto and spontaneouslyhypertensive rat strains and humans, suggesting that this phenomenon isa characteristic of proximal tubule cells. The electrical currentinduced in intact monolayers by Ala-Asp, a representative of theseacidic dipeptides, must representCl secretion rather thanNa⁺ orH⁺ absorption, because1) it wasNa⁺ independent,2) it showed a pH dependencedifferent from that of the PEPT2 cotransporter, and3) it correlated with anAla-Asp-induced increase inCl conductance of theapical membrane in basolaterally amphotericin B-permeabilizedmonolayers. The secretory current could be inhibited by stilbenedisulfonates, but not diphenylamine-2-carboxylates, suggesting anon-cystic fibrosis transmembrane conductance regulator type ofCl conductance. The effectof Ala-Asp was dose dependent, with an apparent 50% effectiveconcentration of ~1 mM. Ala-Asp also produced intracellularacidification, suggesting that acidic dipeptides are also substratesfor an H⁺-peptide cotransporter.