An L-proline-dependent proton flux is located at the apical membrane level of the eel enterocytes.
This study has demonstrated the existence of an L-proline-dependent (Na independent) proton flux at the apical membrane level of the eel intestinal absorbing cells. Using isolated eel enterocytes and the pH-sensitive fluorescent dye 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF), it was shown that a 20 mM concentration of the imino acid L-proline in the extracellular medium determined an intracellular acidification of approximately 0.28 pH units. However, neither sucrose nor other amino acids were able to significantly acidify the resting intracellular pH. A hyperbolic relationship between extracellular proline concentration and intracellular proton accumulation was observed. Using both isolated brush-border and basolateral membrane vesicles, it was demonstrated that this proline-proton cotransport mechanism was located at the apical membrane level only. In addition, the existence of a coupling mechanism between proline and proton fluxes was demonstrated by the observation that, in brush-border membrane vesicles, the presence of a pH gradient (pH(in) > pH(out)) stimulated the uptake of L-proline.
Ingrosso
L
L
Laboratorio di Fisiologia Generale e Comparata, Dipartimento di Biologia Università di Lecce, Monteroni 73100 Lecce, Italy.
Marsigliante
S
S
Zonno
V
V
Storelli
C
C
Vilella
S
S
D026921:Amino Acid Transport Systems, Neutral; D000811:Anguilla; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D020895:Enterocytes / Q000648:ultrastructure*; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000187:drug effects*; D008871:Microvilli / Q000737:chemistry / Q000378:metabolism; D011392:Proline / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D011522:Protons; D012964:Sodium / Q000494:pharmacology; D014316:Tritium
D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D011522:Protons; C041832:proline transport protein; D014316:Tritium; D011392:Proline; D012964:Sodium