Abstract
Purpose: :
The main aim of this study was to identify the presence of folate receptor/transporter carrier-mediated system and to delineate its uptake mechanism across rabbit corneal epithelial cell line (SIRC) and rabbit cornea which acts as an invitro and exvivo model for studying corneal drug delivery respectively.
Methods: :
Uptake of [3H] Folic acid was determined at different time intervals. Effect of temperature on the uptake of folic acid was performed. Concentration dependent studies were carried out with unlabelled folic acid. Folic acid uptake was also studied in presence of structural analogs such as methyltetrahydro folate (MTF) and methotrexate (MTX), vitamins, metabolic inhibitors like ouabain,2,4-dinitrophenol and sodiumazide to delineate the mechanism of uptake. Reverse transcription polymerase chain reaction (RT-PCR) was performed to confirm the molecular identity of folate carrier systems on SIRC and rabbit cornea.
Results: :
Time dependent studies on folate uptake showed linearity up to 30min.Significant inhibition in the uptake of [3H] folic acid was observed at 40C indicating the presence of folate carrier mediated system.Concentartion dependent studies had shown significant inhibition in the uptake of folic acid in the presence of unlabelled folic acid. Folate uptake was inhibited by the structural analogs, MTF and MTX, but not by structurally unrelated vitamins. Uptake was found to be reduced in the presence of metabolic inhibitors suggesting energy dependence for folate uptake. In the presence of colchicine (endocytosis inhibitor) significant inhibition in the [3H] Folic acid uptake was seen indicating the involvement of receptor mediated endocytosis process. RT-PCR analysis had proved the presence of folate receptor on the surface of rabbit corneal epithelial cell line (SIRC) and rabbit cornea.
Conclusions: :
The results of the functional and molecular evidence prove the existence of a specialized carrier-mediated system for folic acid uptake in rabbit intact corneas as well as SIRC cell line.
Keywords: cornea: epithelium • receptors