Guanylate cyclase activity in retina optic nerve and optic chiasm of rats under different illumination conditions.

In the present work we have measured the guanylate cyclase activity in soluble fractions from several tissues relevant to the visual response under different illumination conditions. Guanylate cyclase was sensitive to changes of light/dark periods in incubated extract obtained from soluble fractions of retina, optic nerve and optic chiasm. The changes in soluble guanylate cyclase activity found, about 100 fold between dark and light periods in those tissues, indicate a key role for this enzyme. The results showed that light inhibit strongly the soluble retinal guanylate cyclase activity; while it increases the activity of this enzyme in the optic nerve. A generalized photoinhibited response of soluble guanylate cyclase was observed in all studied tissues in prolonged dark adapted animals. The effect of Na+ 1 and 10 mM, and free Ca++ 28 eta M and 2.8 microM on the guanylate cyclase activity was performed in the studied tissues. The enzymatic activity appeared to be inversely related in the retina and optic nerve with regard to the ion exposure, which may involve different ionic control mechanisms. All indicate an active role for the soluble guanylate cyclase in the phototransduction process not only in retina, also in other tissues relevant in the visual response.