Movement of carboxyfluorescein across the isolated rabbit irisciliary body

Abstract

The movement of carboxyfluorescein across the isolated irisciliary body of the albino rabbit was analyzed using an Ussing chamber under short-circuit conditions with carboxyfluorescein concentrations ranging from 10 to 100 μM.

At a concentration of 50 μM, the outward permeability (from the aqueous to the stromal side) was 4.0 ± 0.2 × 10⁻⁶ cm/sec and the inward permeability (from the stromal to the aqueous side) was 1.3 ± 0.2 × 10⁻⁶cm/sec (Mean ± SE, N = 6). The former was significantly greater than the latter (P < 0.001). Inward movement of carboxyfluorescein showed a linear increase in relation to the concentrations tested. Neither ouabain (100 μM), 2,4-dinitrophenol (10 μM) nor probenecid (100 μM) significantly inhibited the inward movement of carboxyfluorescein.

The net outward movement of carboxy-fluorescein became saturated, as concentration was increased, and a Lineweaver-Burke plot gave an apparent K_m of 28 μM and V_max of 0.67 × 10⁻⁹ mole/hr/cm². In addition, outward carboxyfluorescein movement was signficantly inhibited by ouabain (100 μM), 2,4-dinitrophenol (10 μM), probenecid (100 μM), iodipamide (1.0 mM), hippurate (1.0 mM), low temperature or low external Na⁺ concentration. These results suggest that outward carboxyfluorescein movement across the tissue largely depends on carrier-mediated active transport, while inward movement occurs by passive diffusion. Curr.

Key Words:

• carboxyfluorescein
• carrier-mediated transport
• irisciliary body
• Lineweaver-Burke plots
• Ussing chamber