Ascorbic acid transport by intestinal brush-border membrane vesicles of the teleost Anguilla anguilla.
Transport of L-ascorbate by intestinal brush-border membrane vesicles of European eel Anguilla anguilla was stimulated by a transmembrane Na gradient (out > in) but not by a similarly directed gradient of K. Under short-circuited membrane potential conditions, a kinetic analysis of L-ascorbate influx indicated the presence of a single Na-dependent carrier process (Kapp = 0.75 +/- 0.07 mM and Jmax = 0.33 +/- 0.03 nmol.mg protein-1.min-1) and a nonsaturable transfer component with an apparent diffusional permeability (P) of 0.27 +/- 0.02 microliter.mg protein-1.min-1. D-Isoascorbate was a competitive inhibitor of L-ascorbate influx exhibiting a Ki of 8.21 +/- 0.63 mM. The electrogenic nature of +Na-L-ascorbate cotransport was confirmed by a stimulatory effect of an inside-negative membrane potential on vitamin uptake. Hill analysis of L-ascorbate influx over a wide range of external Na concentrations suggested a 2 Na-to-1 L-ascorbate binding ratio. Results indicate that the vitamin L-ascorbate is transported across fish intestinal brush-border membranes by an electrogenic Na-dependent carrier process in conjunction with more than one sodium ion.
Maffia
M
M
Dipartimento di Biologia, Universita di Lecce, Italy.
Ahearn
G A
GA
Vilella
S
S
Zonno
V
V
Storelli
C
C
D000818:Animals; D001205:Ascorbic Acid / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002412:Cations / Q000494:pharmacology; D004524:Eels / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000502:physiology; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D008954:Models, Biological; D009994:Osmolar Concentration; D012964:Sodium / Q000493:pharmacokinetics / Q000494:pharmacology; D013997:Time Factors
D002412:Cations; D012964:Sodium; D001205:Ascorbic Acid