CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE

Abstract

Cyclic nucleotides have been implicated in the differentiation and function of the vertebrate retina. In the normal retina of DBA mice, the specific activity of cyclic-nucleotide phosphodiesterase (PDE), with cyclic-AMP as the substrate (cAMP-PDE), increases eightfold between the 6th and 20th postnatal day. Kinetic analysis of retinae from newborn mice reveals a PDE with a single Michaelis constant (Km) value for cyclic-AMP (low Km-PDE). After the 6th postnatal day, a second PDE with a high Km for cyclic-AMP (high Km-PDE) can be demonstrated. The appearance and increasing activity of the high Km-PDE coincides with the differentiation and growth of photoreceptor outer segments. Additionally, the high Km-PDE is shown by microchemical techniques to be concentrated in the photoreceptor cell layer and the low Km-PDE within the inner layers of the normal retina. In C3H mice afflicted with an inherited degeneration of the photoreceptor layer, the postnatal increase in the specific activity of cAMP-PDE is substantially lower than in the normal retina. The postnatal increase in the specific activity of cAMP-PDE in two regions of the brain of C3H mice is the same as in the normal strain. A deficiency in high Km-PDE activity in the C3H retina is evident on the 7th postnatal day, when the activity of low Km-PDE, photoreceptor morphology, and rhodopsin content of these retina are essentially normal. In the adult C3H retina, the PDE activity with cyclic-GMP and cyclic-UMP as substrates is significantly below that of the normal retina. These data indicate that an alteration in cyclic-AMP metabolism occurs before photoreceptor cell degeneration in the retinae of C3H mice.