Transport of L-carnitine in human corneal and conjunctival epithelial cells

[摘要] Purpose: Previously we demonstratedexpression and localization of carnitine/organic cation transporters,OCTN1 and OCTN2, in human corneal and conjunctival epithelia. Thepresent study aimed to examine the characteristics of L-carnitinetransporters in cultured human limbal corneal (HCLE) and conjunctivalepithelial (HCjE) cells. Methods: Time-course, Na+-dependence,kinetics,energy- and pH- dependence of L-carnitine transport wereinvestigated by monitoring L-[3H]carnitine uptake into HCLEand HCjE cells. To determine the specificity of action, competition andinhibition studies were performed. Results: The uptake of L-carnitine intoHCLE and HCjE cells was saturable and time-dependent. An Eadie-Hofsteeplot showed two distinct components: a high- and a low- affinitycarnitine transport system in HCLE and/or HCjE cells. L-carnitinetransport was significantly inhibited by the metabolic inhibitors(sodium azide, dinitrophenol, iodoacetic acid). The L-carnitine analogs(D-carnitine, acetyl-L-carnitine and γ-butyrobetaine),tetraethylammonium (TEA), 2-amino-2-norbornane carboxylic acid (BCH),strongly inhibited uptake of L-[3H]carnitine. Uptake of L-[3H]carnitinealsorequired the presence of Na+ in the external medium andthe uptake activity was maximal at pH 5.5. The anti-OCTN2 antibodyblocked L-carnitine uptake in both HCLE and HCjE cells whereas theanti-OCTN1 antibody did not significantly block L-carnitine uptake. Conclusions: L-carnitine is transportedinto HCLE and HCjE cells by an active carrier mediated transport systemthat is time-, Na+-, energy- and pH- dependent. Thecarnitine/organic cation transporter OCTN2 appears to play a dominantrole in this process.

[学科分类] 生物化学/生物物理