Calcium and cyclic nucleotide regulation in incubated mouse retinas.

Abstract

When retinas from dark-adapted C57BL/6 mice were incubated in the dark for 5 rain at 37~ in Earle's medium, they contained 80-120 pmol/mg protein of cGMP and about 13 pmol/mg protein of cAMP. When the incubation in darkness was in calcium-deficient Earle's medium with 3 mM EGTA, a 10-20-fold increase occurred in the cGMP level, peaking at 2-3 min, but no change occurred in cAMP. This elevated level fell in 3 min to normal dark levels on return to normal Earle's medium, but was still about three times that of control levels after 15 rain in EGTA-containing solution. Bright light after 2 min of dark incubation of darkadapted retinas resulted in a 40-50% fall in cGMP, and bright light sharply reduced the elevated dark cGMP level of retinas in calcium-deficient media with 3 mM EDTA. However, no depression of normal dark levels of cGMP has thus far been obtained by increasing external calcium levels, even in the presence of the ionophore A23187. All the above phenomena involving dark cGMP levels and calcium are similar in Earle's medium with 100 mM of K + substituted for Na +. Congenic rodless (rd/rd) mouse retinas have <5% of control cGMP and show only traces of calcium sensitivity. Thus, the above phenomena in controls are likely to be largely occurring in rods. The data suggest a dependency of the dark cGMP level on the calcium level, but that the light-induced fall in cGMP may largely be calcium insensitive.

Effects of calcium and guanosine‐3',5'‐cyclic‐monophosphoric acid on receptor potentials of toad rods.

“…First, the procedures used to change the internal concentration of Ca2+ and cGMP may affect other cell functions (Bianchi, 1961;Sheppard, 1970;Plagemann, 1974;Gaska, Canter & Shelanski, 1975;Klausner, Bhalla, Dragsten, Hoover & Karnovsky, 1980). A second problem is that cGMP and Ca2+ may play interacting roles in rod physiology since changes in the concentration ofone change the concentration ofthe other (Cohen et al 1978;Kilbride & Ebrey, 1979;Kilbride, 1980;Polans et al 1981). Despite these complications, the present results can be used to help either validate or invalidate some of the currently popular models of photoreceptor excitation.…”

“…Cohen, Hall & Ferrendelli (1978) showed that incubation of mouse retinas in a Ca-deficient medium results in increased levels of cGMP. In the present study the concentration of Ca2+ in the perfusate was decreased, and the intracellular cyclic nucleotide concentration was increased either by ionophoresis or by addition of a PDE inhibitor.…”

Light adaptation in toad rods: requirement for an internal messenger which is not calcium.

“…Their experiments (Yoshikami & Hagins, 1973;Hagins & Yoshikami, 1974) and those of others (Brown & Pinto, 1974;Winkler, 1974;Lipton et al 1977;Bertrand et al 1978), including the ones we have described in this paper, are consistent with the notion that changes in internal Ca2+ concentration alter g1. Ca2+ could do this directly by binding to light-dependent channels in the plasma membrane (Hagins, 1972), or indirectly by changing intracellular pH (Meech & Thomas, 1977), the concentration of cyclic nucleotides (Cohen, Hall & Ferrendelli, 1978;Woodruff & Bownds, 1979), or the rate of some enzymatic reaction (Greengard, 1978).…”

Cytochemical demonstration of guanylate cyclase activity in retinal photoreceptors with special reference to changes under light and dark adaptation.

“…In view of the evidence of these studies, cyclic GMP is considered to be one of the possible visual transmitters that could transfer information from the site of photon absorption in the disc membranes to the permeability mechanism in the plasma membrane (16,27). Other studies (6,11,21) suggest an interrelation between cyclic GMP and a calcium ion which is considered to be another probable transmitter (26) . It is also possible that cyclic GMP plays an important role in visual adaptation, with changes in cyclic GMP modifying the effect of illumination on the permeability mechanism (29,34) .…”

“…In the dark, the cyclic GMP level in the rod outer segments is high, and illumination causes a decrease in the level of cyclic GMP in the whole retina (11,25,29,35), in photoreceptor cells (36), and in isolated outer segments (21,49,50), apparently through activation of the degradation enzyme, cyclic GMP-phosphodiesterase (9,24,33,48) . In view of the evidence of these studies, cyclic GMP is considered to be one of the possible visual transmitters that could transfer information from the site of photon absorption in the disc membranes to the permeability mechanism in the plasma membrane (16,27).…”