Effect of AQP1 expression level on CO2 permeability in bovine corneal endothelium

PURPOSE. Corneal endothelial fluid transport is dependent on HCO3- and CO2 fluxes. CO2 permeability (Pco(2)) measurements in an oocyte expression syst em and in reconstituted proteoliposomes have suggested that the water chann el AQP1 can transport CO2. An AQP1 knockout mouse model, however, showed no evidence for CO2 transport through AQP1 in erythrocytes or lung. Because H CO3- and CO2 fluxes are essential to endothelial function, the current stud y was conducted to determine whether AQP1 expression levels in confluent cu ltures of bovine corneal endothelial cells (BCECs) affects membrane Pco(2). METHODS. BCEC endogenous AQP1 expression was reduced by antisense oligonucl eotide (AO) transfection or adenoviral antisense-AQP1 (AV) infection. AQP1 was overexpressed by adenoviral sense-AQP1 (SV) infection, which directs ex pression of recombinant AQP1. RESULTS. Expression of AQP1 and osmotic water permeability (control P-f= 0. 046 +/- 0.005 cm/sec) were reduced 45% and 36.5%, respectively, by AO trans fection and reduced 67% and 49%, respectively, by AV infection. SV infectio n induced a more than threefold overexpression of AQP1 but showed only a 37 % increase in P-f. Adenoviral empty virus (EV) infection did not change AQP 1 expression or P-f. Pco(2) was determined by measuring the rate of intrace llular pH decrease after exposure to CO2/HCO3--rich solutions, as measured by the pH-sensitive fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-ca rboxyfluorescein. (BCECF). Apparent Pco(2) of BCEC (0.0036 +/- 0.00023 cm/s ec) was not different among control, oligonucleotide-transfected, and adeno viral-infected cells. P-f could also be reduced more than 50% by 3 to 5 min utes' exposure of control cells to 0.5 mM p-chloromercuriphenylsulfonic aci d (pCMBS), but this had no effect on rates of intracellular pH decrease. CONCLUSIONS. AQP1 does not contribute to Pco(2) in corneal endothelial cell s.