H(+)-peptide cotransport in Madin-Darby canine kidney cells: expression and calmodulin-dependent regulation

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Abstract
The transport of the dipeptide glycylsarcosine was studied in the kidney cell lines OK, LLC-PK1, and Madin-Darby canine kidney (MDCK), grown as confluent monolayers on impermeable plastic supports. Uptake of the dipeptide in OK and LLC-PK1 cells was slow, was not inhibited by other peptides, and was not influenced by an inwardly directed H+ gradient, indicating lack of expression of the H(+)-peptide cotransport system in these cells under our conditions. In contrast, uptake of the dipeptide in MDCK cells was rapid and was found to be stimulated by an inwardly directed H+ gradient. This stimulation was markedly reduced by the protonophore carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. The H+ gradient-dependent uptake of glycylsarcosine was inhibited by dipeptides and tripeptides and by the beta-lactam antibiotic cephalexin but not by the amino acids glycine and leucine. The uptake was saturable and apparently occurred via a single transport system. The Michaelis-Menten constant for the system was 1.3 +/- 0.1 mM, and the maximal velocity was 13.3 +/- 0.7 nmol.30.min-1.mg protein-1. Treatment of MDCK cells with the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide (W-7), CGS-9343B, or calmidazolium inhibited the glycylsarcosine uptake by 40-50% in a time- and dose-dependent manner. In contrast, the uptake of alanine, leucine, glucose, and taurine was found to be stimulated by treatment with W-7. Kinetic analysis revealed that the inhibition of the peptide transport activity was mainly associated with a decrease of the maximal velocity of the system.(ABSTRACT TRUNCATED AT 250 WORDS)

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