Calcium effects on frog retinal cyclic guanosine 3′, 5′-monophosphate levels and their light-initiated rate of decay

Abstract

When retinal sections were isolated from dark-adapted bullfrogs and placed in normal Ringer’s solution, they contained 40.7 ± 0.2 pmol cGMP/ mg protein (mean :t: SEM, 30 samples). When isolated, dark-adapted retinal sections were removed from normal Ringer’s solution and placed in calciumdeficient Ringer’s solution with 3 mM EGTA, there was about a threefold rise in cyclic GMP (cGMP) levels by 1.5 min and about a 10-fold rise by 5 rain. The cGMP level remained high with no detectable decrease for at least 40 min (the longest time measured). When isolated, dark-adapted retinal sections were removed from normal Ringer’s solution and placed in Ringer’s solution which contained high-calcium (20 mM CaCl2), there was a slow but significant decrease in cGMP levels. After 20 rain in high-calcium Ringer’s solution the cGMP level was 0.58 ± 0.07 (mean + SEM, eight samples) of the cGMP level in normal Ringer’s solution incubated for the same time. The rate at which 10- fold elevated cGMP levels in low calcium decreased upon illumination was examined using quick-freezing techniques on the retinal sections. The elevated cGMP level in retinal sections incubated in low-calcium Ringer’s solution was found to decay about 15-fold faster than cGMP levels in retinal sections incubated in normal Ringer’s solution. The cGMP level in low calcium was significantly different (P = 0.005) after 1 s illumination, whereas the cGMP level in normal calcium was not significantly different. © 1980, Rockefeller University Press., All rights reserved.