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

Mol Vis. 2010 Sep 4;16:1823-31.


Purpose: Previously we demonstrated expression and localization of carnitine/organic cation transporters, OCTN1 and OCTN2, in human corneal and conjunctival epithelia. The present study aimed to examine the characteristics of L-carnitine transporters in cultured human limbal corneal (HCLE) and conjunctival epithelial (HCjE) cells.

Methods: Time-course, Na(+)-dependence, kinetics, energy- and pH- dependence of L-carnitine transport were investigated by monitoring L-[(3)H]carnitine uptake into HCLE and HCjE cells. To determine the specificity of action, competition and inhibition studies were performed.

Results: The uptake of L-carnitine into HCLE and HCjE cells was saturable and time-dependent. An Eadie-Hofstee plot showed two distinct components: a high- and a low- affinity carnitine transport system in HCLE and/or HCjE cells. L-carnitine transport 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-[(3)H]carnitine. Uptake of L-[(3)H]carnitine also required the presence of Na(+) in the external medium and the uptake activity was maximal at pH 5.5. The anti-OCTN2 antibody blocked L-carnitine uptake in both HCLE and HCjE cells whereas the anti-OCTN1 antibody did not significantly block L-carnitine uptake.

Conclusions: L-carnitine is transported into HCLE and HCjE cells by an active carrier mediated transport system that is time-, Na(+)-, energy- and pH- dependent. The carnitine/organic cation transporter OCTN2 appears to play a dominant role in this process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport Systems / genetics
  • Amino Acid Transport Systems / metabolism
  • Antibodies / pharmacology
  • Biological Transport / drug effects
  • Carnitine / analogs & derivatives
  • Carnitine / metabolism*
  • Cations / pharmacology
  • Cell Line
  • Conjunctiva / cytology*
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism*
  • Epithelium, Corneal / cytology*
  • Gene Expression Regulation / drug effects
  • Humans
  • Hydrogen-Ion Concentration / drug effects
  • Kinetics
  • Norbornanes / pharmacology
  • Organic Cation Transport Proteins / immunology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Sodium / pharmacology
  • Solute Carrier Family 22 Member 5
  • Symporters
  • Temperature
  • Time Factors


  • Amino Acid Transport Systems
  • Antibodies
  • Cations
  • Norbornanes
  • Organic Cation Transport Proteins
  • RNA, Messenger
  • SLC22A4 protein, human
  • SLC22A5 protein, human
  • Solute Carrier Family 22 Member 5
  • Symporters
  • Sodium
  • Carnitine