Dipeptide uptake by adenohypophysial folliculostellate cells.
Dipeptide uptake was studied in primary cultures from rat anterior pituitaries by use of radiolabeled carnosine and the fluorescent dipeptide derivative beta-Ala-Lys-N epsilon-AMCA (AMCA is 7-amino-4-methylcoumarin-3-acetic acid). Fluorescence microscopic studies revealed that the reporter peptide specifically accumulated in the S-100 positive folliculostellate cells that do not produce any known hormone. The dipeptide derivative was taken up in unmetabolized form by an energy-dependent saturable process with apparent kinetic constants as follows: Michaelis constant, 19 microM; maximum velocity, 5.5 nmol.mg protein-1.h-1. This high-affinity transporter was strongly affected by inhibitors of sodium/proton exchangers and thus appeared to be driven by a proton gradient. Competition studies revealed that the peptide transporter exhibits broad substrate specificity with a preference for hydrophobic dipeptides. In contrast to free amino acids and the pseudotetrapeptide amastatin, tripeptides were also accepted. Compounds without an alpha- and beta-amino group, such as captopril, thiorphan, and benzylpenicillin, did not affect uptake of the reporter peptide, although they were substrates of the well-characterized intestinal and renal dipeptide transporters.
Otto
C
C
Max-Planck-Institut für Experimentelle Endokrinologie, Hannover, Germany.
tom Dieck
S
S
Bauer
K
K
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D002336:Carnosine / Q000493:pharmacokinetics; D002478:Cells, Cultured; D003374:Coumarins / Q000493:pharmacokinetics; D004151:Dipeptides / Q000493:pharmacokinetics*; D004734:Energy Metabolism; D005260:Female; D005456:Fluorescent Dyes; D006651:Histocytochemistry; D009994:Osmolar Concentration; D010455:Peptides / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D013997:Time Factors
D000596:Amino Acids; D003374:Coumarins; D004151:Dipeptides; D005456:Fluorescent Dyes; D010455:Peptides; D017923:Sodium-Hydrogen Exchangers; D002336:Carnosine; C051029:7-amino-4-methylcoumarin-3-acetic acid