L-Carnitine transport in mouse renal and intestinal brush-border and basolateral membrane vesicles.
We characterized the uptake of carnitine in brush-border membrane (BBM) and basolateral membrane (BLM) vesicles, isolated from mouse kidney and intestine. In kidney, carnitine uptake was Na(+)-dependent, showed a definite overshoot and was saturable for both membranes, but for intestine, it was Na(+)-dependent only in BLM. The uptake was temperature-dependent in BLM of both kidney and intestine. The BBM transporter in kidney had a high affinity for carnitine: apparent K(m)=18.7 microM; V(max)=7.85 pmol/mg protein/s. In kidney BLM, similar characteristics were obtained: apparent K(m)=11.5 microM and V(max)=3.76 pmol/mg protein/s. The carnitine uptake by both membranes was not affected within the physiological pH 6.5-8.5. Tetraethylammonium, verapamil, valproate and pyrilamine significantly inhibited the carnitine uptake by BBM but not by BLM. By Western blot analysis, the OCTN2 (a Na(+)-dependent high-affinity carnitine transporter) was localized in the kidney BBM, and not in BLM. Strong OCTN2 expression was observed in kidney and skeletal muscle, with no expression in intestine in accordance with our functional study. We conclude that different polarized carnitine transporters exist in kidney BBM and BLM. L-Carnitine uptake by mouse renal BBM vesicles involves a carrier-mediated system that is Na(+)-dependent and is inhibited significantly by specific drugs. The BBM transporter is likely to be OCTN2 as indicated by a strong reactivity with the anti-OCTN2 polyclonal antibody.
Lahjouji
Karim
K
Division of Medical Genetics, Hôpital Sainte-Justine, 3175 Cote Sainte-Catherine, H3T 1C5, Montreal, QC, Canada.
Malo
Christiane
C
Mitchell
Grant A
GA
Qureshi
Ijaz A
IA
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015153:Blotting, Western; D002331:Carnitine / Q000172:deficiency / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D051379:Mice; D008871:Microvilli / Q000378:metabolism; D027701:Organic Cation Transport Proteins; D000074058:Solute Carrier Family 22 Member 5; D013696:Temperature; D013997:Time Factors
D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027701:Organic Cation Transport Proteins; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; D002331:Carnitine