Abstract: Objective To investigate the characteristics of L-carnitine (LC)import into human corneal limbal epithelia (HCLE)cells,and to provide an experimental basis for further study of transport mechanism of LC in human ocular epithelium.Methods The transport of [3 H ]-L-carnitine was determined using the radio uptake assay and the apparent kinetic parameters of carnitine uptake by HCLE were estimated by nonlinear regression curve fitting according to the Michaelis-Menten equation.Results The uptake of LC into HCLE cells was saturable and time-dependent,and it also required the presence of Na+ in the external medium.An Eadie-Hofstee plot showed two distinct components:a high-and a low-affinity carnitine transport system in HCLE cells.The unlabelled LC and acetyl-L-carnitine competitively inhibited the uptake of [3 H]-L-carnitine by HCLE cells.Conclusion L-carnitine is transported into HCLE cells from tears by an active carrier mediated transport system and exerts its biological function.

Key words: L-carnitine, epithelium, corneal, transcytosis