Document Detail


Transport of L-carnitine in human corneal and conjunctival epithelial cells.
MedLine Citation:
PMID:  21045919     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
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.
Authors:
Shunjiang Xu; Judith L Flanagan; Peter A Simmons; Joseph Vehige; Mark D Willcox; Qian Garrett
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2010-09-04
Journal Detail:
Title:  Molecular vision     Volume:  16     ISSN:  1090-0535     ISO Abbreviation:  Mol. Vis.     Publication Date:  2010  
Date Detail:
Created Date:  2010-11-03     Completed Date:  2011-02-08     Revised Date:  2013-07-03    
Medline Journal Info:
Nlm Unique ID:  9605351     Medline TA:  Mol Vis     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1823-31     Citation Subset:  IM    
Affiliation:
Brien Holden Vision Institute, The University of New South Wales, Sydney, NSW, Australia.
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MeSH Terms
Descriptor/Qualifier:
Amino Acid Transport Systems / genetics,  metabolism
Antibodies / pharmacology
Biological Transport / drug effects
Carnitine / analogs & derivatives,  metabolism*
Cations / pharmacology
Cell Line
Conjunctiva / cytology*
Epithelial Cells / drug effects,  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,  metabolism
Sodium / pharmacology
Temperature
Time Factors
Chemical
Reg. No./Substance:
0/Amino Acid Transport Systems; 0/Antibodies; 0/Cations; 0/Norbornanes; 0/Organic Cation Transport Proteins; 0/RNA, Messenger; 0/SLC22A4 protein, human; 0/SLC22A5 protein, human; 541-15-1/Carnitine; 7440-23-5/Sodium
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