Fluid transport across cultured layers of corneal endothelium from aquaporin-1 null mice

Abstract

We explored the role of AQP1, the only known aquaporin in corneal endothelium, on active fluid transport and passive osmotic water movements across corneal endothelial layers cultured from AQP1 null mice and wildtype mice. AQP1 null mice had grossly transparent corneas, just as wildtype mice. Endothelial cell layers grown on permeable supports transported fluid at rates of (in μl h −1 cm −2, n=9, mean± s.e.): 4·3±0·6, wildtype mice (MCE); 3·5±0·6, AQP1 null mice (KMCE; difference not significant). The osmotic water flow (also in μl h −1 cm −2) induced by a 100 mOsm sucrose gradient across MCE cell layers (8·7±0·6, n=8) was significantly greater than that across KMCE (5·7±0·7, n=6, p=0·007). When plated on glass coverslips, plasma membrane osmotic water permeability determined by light scattering was significantly higher for cells from wildtype vs. AQP1 null mice (in μm sec −1: 74±4, n=19 vs. 44±4 μm sec −1, n=11, p<0·001). Unexpectedly, after 10% hypo-osmotic challenge, the extent of the regulatory volume recovery was significantly reduced for AQP1 null mice cells (in%: MCE controls, 99±1, n=19, vs. KMCE: 64±5, n=11, p<0·001). Thus, as in other ‘low rate’ fluid transporting epithelia, deletion of AQP1 in mice corneal endothelium reduces osmotic water permeability but not active transendothelial fluid transport. However, that deletion impaired the extent of regulatory volume decrease after a hypo-osmotic challenge, suggesting a novel role for AQP1 in corneal endothelium.