Spontaneous calcium-independent nitric oxide synthase activity in porcine ciliary processes.

In the cornea, iris, retina, and ciliary processes of porcine eyes the nitric oxide synthase (NOS) activity was assayed by measuring the transformation of L-[U-14C]-arginine into L-[U-14C]-citrulline: (1) in the absence or presence of the calcium-chelator, ethylene glycol tetra acetic acid (EGTA), and (2) in the presence of EGTA and the false precursor of L-arginine, NG-nitro-L-arginine methyl ester (L-NAME). In the retina and the iris a high calcium-dependent NOS activity was present, while in the cornea the activity was relatively low. In these three tissues no significant calcium-independent NOS activity was detected. In contrast, a marked calcium-independent NOS activity, but no calcium-dependent NOS activity, was found in the ciliary processes. The presence of a spontaneous calcium-independent NOS activity in the ciliary processes suggests that nitric oxide (NO) production is highly regulated in this tissue.