Guanosine 3',5'-cyclic monophosphate and the in vitro physiology of frog photoreceptor membranes (original) (raw)
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EFFECTS OF LIGHT ON CYCLIC GMP METABOLISM IN RETINAL PHOTORECEPTORS
Journal of Neurochemistry, 1976
Abstract— Guanylate cyclase activity of dark-adapted bovine rod outer segments demonstrates a biphasic pattern upon exposure to light. By 10 s of illumination, activity is 20% lower than that observed in dark-adapted outer segments. Activity subsequently increases and then slowly declines to two-thirds of the original activity after 10 min of illumination. In the presence of GTP or ATP, hydrolysis of cyclic GMP is rapidly enhanced by exposure of outer segments to light; the magnitude of this effect is dependent on the amount of substrate present. The rapid effects of light on synthesis and degradation of cyclic GMP indicate that these reactions may be involved in the visual process. The concentration of guanosine 3′:5′-cyclic monophosphate (cyclic GMP) is extraordinarily high in dark-adapted bovine rod outer segments and is at least 100-fold that of adenosine 3′:5′-cyclic monophosphate (cyclic AMP). No significant decrease in the level of cyclic GMP or cyclic AMP was observed however upon exposure of dark-adapted outer segments to light.
Effect of light and calcium on cyclic GMP synthesis in rod outer segments of toad retina
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1986
The rod outer segments of toad retina contain a guanylate cyclase activity of about 3 + 1 nmol of cGMP formed/min per mg protein. In darkness this value is largely independent of the Ca 2+ concentration, although it is enhanced by light upon lowering the Ca 2+ concentration from 10-s to 10-8 M. The activating effect of light on cyclase at low Ca 2+ concentrations is enlarged upon increasing the light intensity. With a flash of light bleaching 7 • 10 -2 percent of rhodopsin, cyclase activity increased by a factor of 30 when Ca 2+ levels dropped from 10-s to 10-8 M. In view of recent observations that shortly after a flash of light the calcium activity inside the photoreceptor cell decreases, it seems likely that Ca 2 ÷ plays a regulatory role on cGMP metabolism in visual excitation.
Search for a physiological role of cyclic GMP metabolism in the photoreceptors
Neurochemistry International, 1980
Data on the time-course of the light-activation of the cyclic GMP phosphodiesterase and of the GTPase, and results on the influence of cyclic GMP on the disc membrane permeability are presented. On the basis of the kinetic data, it is not possible to separate the light-activation of these two enzymes from the early steps of photoreceptor transduction. In addition, the cyclic GMP increases the permeability of the disc membranes, indicating that a decrease of the endogenous cyclic GMP concentration, consequent to the light-activation of the phosphodiesterase, can de~ crease the membrane permeability shortly after illumination.
Dynamics of Cyclic GMP Synthesis in Retinal Rods
Neuron, 2002
, 2 1989). As a result, the intracellular [Ca 2ϩ ] falls. This drop and Denis A. Baylor 1 in [Ca 2ϩ ] causes coordinated changes that antagonize 1 Department of Neurobiology the response to light. The Ca 2ϩ signal is thought to de-Stanford University Medical Center crease rhodopsin activity (Kawamura and Murakami, Stanford, California 94305 1991), increase the sensitivity of the channel for cGMP 2 The Mary D. Allen Laboratory for Vision Research (Hsu and Molday, 1993), and increase the activity of GC Doheny Eye Institute and (Lolley and Racz, 1982). To date, the specific quantita-Departments of Ophthalmology and Cell tive contribution of each Ca 2ϩ-dependent process to rod and Neurobiology function has only been inferred (see Koutalos et al., Keck School of Medicine of the 1995b; Nikonov et al., 2000). We therefore sought to University of Southern California directly determine how rapidly and powerfully Ca 2ϩ feed-Los Angeles, California 90033 back to GC acts in intact rods. 3 Center for Neuroscience and Figure 1 is a diagram of the negative feedback loop Department of Psychiatry that couples the rate of cGMP synthesis to the size of the University of California, Davis inward membrane current. A change in the intracellular Davis, California 95616 [cGMP] rapidly changes the inward current, and thus, the intracellular free [Ca 2ϩ ]. The change in [Ca 2ϩ ] is detected by GCAPs, which alter the rate of synthesis of Summary cGMP to oppose the initial change in [cGMP]. The steady-state gain of the feedback loop, g L , is not known. In retinal rods, Ca 2؉ exerts negative feedback control This parameter is defined as the ratio of the relative on cGMP synthesis by guanylate cyclase (GC). This change in the rate of synthesis of cGMP to the relative feedback loop was disrupted in mouse rods lacking change in the [cGMP], both changes being small. The guanylate cyclase activating proteins GCAP1 and loop gain is perhaps the single most important property GCAP2 (GCAPs Ϫ/Ϫ). Comparison of the behavior of of the loop, for it determines how powerfully small wild-type and GCAPs Ϫ/Ϫ rods allowed us to investigate changes in [cGMP] are nulled in the steady state. Since the role of the feedback loop in normal rod function. the cooperativity of channel activation (n ch) by cGMP is We have found that regulation of GC is apparently the 3 (Haynes et al., 1986; Zimmerman and Baylor, 1986; only Ca 2؉ feedback loop operating during the single Ruiz et al., 1999), a small relative change in [cGMP] will photon response. Analysis of the rods' light responses produce a 3-fold larger change in the relative Ca 2ϩ influx and cellular dark noise suggests that GC normally rein the steady state (see Experimental Procedures). Likesponds to light-driven changes in [Ca 2؉ ] rapidly and wise, if the activation of GCs by GCAPs is linear for highly cooperatively. Rapid feedback to GC speeds small changes in [Ca 2ϩ ], the relative change in the rate the rod's temporal responsiveness and improves its of synthesis will be n GC-fold greater than the relative signal-to-noise ratio by minimizing fluctuations in change in the [Ca 2ϩ ], where n GC is the cooperativity of cGMP. Ca 2ϩ regulation of GCs. Therefore, the ratio of the relative change in the rate of synthesis to the relative change
Journal of Neurochemistry, 1977
The effect of light on the content of cyclic GMP in degenerative retinae of Royal College of Surgeons (RCS) rats and rd mice was compared with that in control retinae during postnatal maturation. In vivo, the cyclic GMP content of retinae of control rats or mice is light-dependent after photoreceptor outer segments develop. Mature retinae of control animals have high levels of cyclic GMP in the dark which are reduced &50% upon illumination. In the rd mouse disorder, a lightinduced reduction in cyclic GMP content is observed while the rod outer segments are morphologically intact. The rd photoreceptor cells possess a phosphodiesterase which, when stabilized by freeze-drying, has a K , similar to that of control photoreceptors, and an apparent V,,, that is below normal. It is suggested that developing rd visual cells have an abnormality in cyclic GMP metabolism which results in the accumulation of cyclic GMP within the entire cell but which does not prevent the light-mediated reduction of cyclic GMP in their outer segment organelles. In the RCS dystrophy, a light-induced reduction in cyclic GMP content is observed also during the period when photoreceptor outer segments are present. The cyclic GMP content of dark-or light-adapted RCS retinae is below that of the respective controls. Biochemical and morphological observations show that cyclic GMP levels increase in rd visual cells and that they are reduced in photoreceptor cells of RCS retina before the onset of visual cell degeneration. Until detailed knowledge of the role of cyclic GMP in the visual cells is known, it is suggested that high or low levels of cyclic GMP in rd and RCS photoreceptors, respectively, result from differences in the etiology or histopathology of the mouse and rat diseases.
Light Inhibition of Bovine Retinal Rod Guanylyl Cyclase Mediated by βγ-Transducin †
Biochemistry, 1999
Photoreceptor guanylyl cyclase (ROS-GC), converting GTP into cGMP and pyrophosphate, is a key enzyme in the regulation of the visual transduction cascade. ROS-GC requires GC-activating proteins (GCAPs) and low free [Ca] for full activity. We found that when choline or potassium were the major cations present, light caused a 70% inhibition of stimulated ROS-GC in native unstripped membranes. In the presence of sodium ions, however, no inhibition was observed. ROS-GC activity of ROS membranes, stripped of transducin and other components, was not affected by light when reconstituted with GCAP1 only. However, when stripped ROS membranes were reconstituted with both GCAP1 and either transducin (T R γ ) or the T γ -subunits, the inhibition of ROS-GC by light was restored. The T R -subunit alone was ineffective. These results suggest that under saturating light conditions, ROS-GC may be regulated by T γ and cations, providing a possible mechanism of desensitization and light adaptation.
Guanylate cyclase in rod outer segments of the toad retina
FEBS Letters, 1986
Guanylate cyclase activity was measured in disrupted rod outer segments of the toad retina. The experiments showed that cGMP is synthesized from GTP at a rate of 3 f 1 nmol/min per mg protein. In darkness this value is largely independent of the CaZ+ concentration, while it is enhanced by flashes of light of increasing intensity upon lowering Ca from lo-' to 10e8 M. In view of recent observations that shortly after a flash of light calcium activity inside the photoreceptor cell decreases, it seems likely that calcium plays a regulatory role in cGMP metabolism in visual excitation.
Melatonin effect on the cyclic GMP system in the golden hamster retina
Brain Research, 1996
Melatonin effect on retinal cyclic GMP accumulation, guanylate cyclase activity, cyclic GMP content and cyclic GMP phosphodiesterase activity was examined in the Syrian hamster retina. Melatonin increased significantly cyclic GMP accumulation at picomolar concentrations and in a time-dependent manner. The kinetic analysis of guanylate cyclase activity revealed a significant increase of both apparent Vma,, and Kr, , induced by 10 nM melatonin. The effect of melatonin was higher in the absence, than in the presence of the phoshodiesterase inhibitor (IBMX), suggesting an effect on cyclic GMP catabolism. Phosphodiesterase activity was significantly decreased by melatonin. The results show a dual effect of melatonin on cyclic GMP levels, i.e. by increasing the synthesis and inhibiting the degradation, both resulting in an increase of cyclic GMP levels. Taking into account the key role of cyclic GMP in visual mechanisms, the results would suggest the participation of melatonin in retinal physiology.
Daily variations in cGMP, guanylate cyclase and phosphodiesterase in the golden hamster retina
Vision Research, 1996
Daily variations in cGMP, guanylate cyclase and phosphodiesterase activity in golden hamster retina were studied. Cyclic GMP content exhibited significant variations throughout the 24.hr cycle with maximal values during the dark phase. In order to establish the relative participation of nucleotide synthesis and breakdown during a 24-hr cycle, guanylate cyclase and phosphodiesterase activity were measured in hamsters killed at eight intervals. Guanylate cyclase activity increased at night, peaking at 22.00 hr. Phosphodiesterase activity did not change significantly throughout the light-dark cycle. Light exposure during the night inhibited the nocturnal increase in cGMP content and guanylate cyclase activity, while phosphodiesterase remained unchanged. From these results, it might be presumed that in response to continuous (in a range of hr) light or dark stimuli, the retina would process the photic signal in a different way from that in the short term (in a range of msec).