Nitric oxide production by isolated human and porcine ciliary processes

Abstract 

Background: In the kidney, the trachea, and the colon, nitric oxide (NO) can modulate transepithelial fluid transport. This study investigates whether isolated human and porcine ciliary processes produce NO.Methods: Porcine ciliary processes and iris were used either fresh or thawed after storage at –70°C. Post-mortem (8–12 h) human ciliary processes were used thawed after storage at –70°C. NO was measured by placing a nafion-coated polymeric porphyrinic microsensor (differential pulse voltammetry) on the surface of the tissue. Measurements were conducted in the absence or in the presence of the NO formation inhibitor N ^G-nitro-l-arginine methyl ester (L-NAME; 0.2 mM, 1 mM) or its biologically inactive d-enantiomer N ^G-nitro-d-arginine methyl ester (D-NAME; 1 mM).  Results: NO concentrations in porcine ciliary processes (1.27±0.25 µM) were higher (P=0.001) than those in the iris (0.00±0.02 µM) and were significantly (P<0.001) decreased by L-NAME (fresh specimen). From thawed porcine ciliary processes, NO concentrations measured (1.85±0.47 µM) were not significantly different (P=0.16) from those measured in fresh specimen and were also reduced (P <0.001) by L-NAME, but not by D-NAME. In human ciliary processes, NO concentrations measured (0.08±0.11 µM) were somehow lower but were again decreased (P<0.001) by L-NAME (thawed specimen).  Conclusion: Reflecting the biological activity of a nitric oxide synthase, isolated human and porcine ciliary processes produce NO.