Functional characterization of intestinal L-carnitine transport.
The carnitine transporter OCTN2 is responsible for the renal reabsorption of filtered L-carnitine. However, there is controversy regarding the intestinal L-carnitine transport mechanism(s). In this study, the characteristics of L-carnitine transport in both, isolated chicken enterocytes and brush-border membrane vesicles (BBMV) were studied. In situ hybridization was also performed in chicken small intestine. Chicken enterocytes maintain a steady-state L-carnitine gradient of 5 to 1 and 90% of the transported L-carnitine remains in a readily diffusive form. After 5 min, L-Carnitine uptake into BBMV overshot the equilibrium value by a factor of 2.5. Concentrative L-carnitine transport is Na+-, membrane voltage-and pH-dependent, has a high affinity for L-carnitine (Km 26 - 31 microM ) and a 1:1 Na+: L-carnitine stoichiometry. L-Carnitine uptake into either enterocytes or BBMV was inhibited by excess amount of cold L-carnitine > D-carnitine = acetyl-L-carnitine = gamma-butyrobetaine > palmitoyl-L-carnitine > betaine > TEA, whereas alanine, histidine, GABA or choline were without significant effect. In situ hybridization studies revealed that only the cells lining the intestinal villus expressed OCTN2 mRNA. This is the first demonstration of the operation of a Na+/L-carnitine cotransport system in the apical membrane of enterocytes. This transporter has properties similar to those of OCTN2.
Durán
J M
JM
Depto. Fisiología y Biología Animal, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain.
Peral
M J
MJ
Calonge
M L
ML
Ilundáin
A A
AA
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology*; D002331:Carnitine / Q000493:pharmacokinetics*; D002352:Carrier Proteins; D002474:Cell-Free System; D002478:Cells, Cultured; D002645:Chickens; D020895:Enterocytes / Q000737:chemistry / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D007421:Intestine, Small / Q000737:chemistry / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins; D008871:Microvilli / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D015336:Molecular Probe Techniques; D027701:Organic Cation Transport Proteins; D011485:Protein Binding; D012680:Sensitivity and Specificity; D012964:Sodium / Q000494:pharmacology; D000074058:Solute Carrier Family 22 Member 5; D013696:Temperature; D022161:Transport Vesicles / Q000378:metabolism
D002352:Carrier Proteins; D008565:Membrane Proteins; D027701:Organic Cation Transport Proteins; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; D012964:Sodium; D002331:Carnitine