Proton-driven dipeptide uptake in primary cultured rabbit conjunctival epithelial cells

Area of Science:

• Ocular pharmacology
• Membrane transport
• Biochemistry

Background:

• Conjunctival epithelial cells play a crucial role in ocular drug absorption.
• Dipeptide uptake mechanisms are vital for ocular drug delivery and efficacy.
• L-carnosine serves as a model dipeptide substrate for transport studies.

Purpose of the Study:

• To characterize the proton-driven, carrier-mediated uptake of L-carnosine in rabbit conjunctival epithelial cells.
• To investigate the kinetic properties and substrate specificity of the dipeptide transporter.
• To explore the potential of this transporter for peptidomimetic drug delivery.

Main Methods:

• Primary conjunctival epithelial cells from pigmented rabbits were cultured.
• Tritiated L-carnosine uptake was measured under various conditions (pH, inhibitors, temperature).
• Computer modeling and stereoisomer inhibition studies evaluated transporter interaction.

Main Results:

• L-carnosine uptake demonstrated directional asymmetry, pH optimum (6.0), and Michaelis-Menten kinetics (Km = 0.3 mM, Vmax = 22.0 pmol/mg protein/min).
• Uptake was inhibited by proton ionophores and NH4Cl, indicating proton dependency.
• Structurally similar dipeptides and drugs inhibited uptake, suggesting transporter promiscuity.

Conclusions:

• A proton-driven dipeptide transporter mediates L-carnosine uptake in conjunctival cells.
• This transporter exhibits characteristics suitable for the delivery of peptidomimetic drugs.
• Understanding this transporter can optimize ocular drug development.