Nitric oxide production by isolated human and porcine ciliary processes

Background: In the kidney, the trachea, and the colon, nitric oxide (NO) ca n 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 a t -70 degrees C. Post-mortem (8-12 h) human ciliary processes were used tha wed after storage at -70 degrees C. NO was measured by placing a nafion-coa ted polymeric porphyrinic microsensor (differential pulse voltammetry) on t he 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 este r (L-NAME; 0.2 mM, 1 mM) or its biologically inactive D-enantiomer N-G-nitr o-D-arginine methyl ester (D-NAME; 1 mM). Results: NO concentrations in por cine ciliary processes (1.27+/-0.25 mu M) were higher (P=0.001) than those in the iris (0.00+/-0.02 mu M) and were significantly (P<0.001) decreased by L-NAME (fresh specimen). From thawed porcine ciliary processes, NO conce ntrations measured (1.85+/-0.47 mu M) 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 mu M) 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 pro cesses produce NO.