Comparison of cyclic nucleotide and energy metabolism of intact mouse retina in situ and in vitro

Whole mouse retina in situ contains approximately 1 μ m adenosine 3′,5′-monophosphate (cyclic AMP) and about fivefold higher levels of guanosine 3′,5′-monophosphate (cyclic GMP). Light-adapted retinas have only half as much of both cyclic nucleotides as dark-adapted retinas. Both cyclic AMP and cyclic GMP levels are modified substantially when retinas are removed from the eye and incubated in physiologic buffers. Cyclic GMP levels increase in light- and dark-adapted retinas, but a differential concentration is always maintained, and after a few minutes of incubation it is even greater than that in in situ retinas. In contrast, the difference between cyclic AMP levels obvious in in situ light- and dark-adapted retinas is obscured during the initial minutes of incubation by a transient rise of cyclic AMP in light-adapted retinas, but then becomes apparent again when cyclic AMP levels fall after about 15 min of incubation. Cyclic AMP and cyclic GMP levels decrease rapidly when isolated dark-adapted retinas, in vitro, are exposed to light and the decrease is a function of light intensity. In contrast, cyclic GMP but not cyclic AMP levels increase when light-adapted retinas, in vitro, are placed in darkness. Ischemia causes a marked reduction of ATP and P-creatine levels and elevates cyclic AMP levels in light- and dark-adapted retinas, in situ. Ischemia depresses cyclic GMP levels in dark-adapted retinas, in situ, but has no effect in light-adapted retinas. In incubated retinas, oxygen deprivation produced by NaCN also decreases energy reserves; however, its effect on cyclic AMP is qualitatively similar to that in vivo only after 15 min of incubation. NaCN has little or no effect on cyclic GMP levels in isolated retinas. These data indicate that cyclic nucleotide regulation in intact, incubated retina has many similarities to that of retina, in vivo, and suggest that with due precautions retina maintained, in vitro, is a valid and useful experimental model system for biochemical and biophysical investigations.