Calcium dependence of the activation and inactivation kinetics of the light-activated phosphodiesterase of retinal rods.

Barkdoll, A. E.; Pugh, Edward N.; Sitaramayya, Ari

doi:10.1085/jgp.93.6.1091

Cited by 36 publications

(16 citation statements)

References 42 publications

(69 reference statements)

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“…Thus, the activity scaled approximately linearly with light intensity, at least over the intensity range we used. This linearity is expected from the results of Barkdoll, Pugh, and Sitaramayya (1989).…”

Section: Phosphodiesterase Activity and Ca "2+ Dependencesupporting

confidence: 74%

The cGMP-phosphodiesterase and its contribution to sensitivity regulation in retinal rods

Koutalos

Nakatani

Yau

1995

The Journal of General Physiology

108

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We have used the truncated outer segment preparation to measure rod cGMP-phosphodiesterase activity, as well as its modulation by Ca 2 § in darkness and in light. The basal enzyme activity in darkness was ~0-3 s -1, and was largely independent of Ca 1+ concentration from 10 nM to 10 ixM. The steady state activity elicited by a step of light (h = 590 nm) was strongly enhanced by Ca 2+, increasing from ~0.005 s-1/(hv Ixm -2 s -1) at 10 nM Ca ~+ to ~0.16 s-l/hv I~m -2 s -1) at 10 IxM Ca 2+. Based on these measurements, as well as previous measurements on the effects of Ca 2+ on rod guanylate cyclase and the cGMP-gated channel, we have calculated the step response-intensity relation for the rod cell in steady state. This relation agrees reasonably well with the relation directly measured from intact rods. We have also evaluated the relative contributions from the three Ca 2+ effects to rod sensitivity. At low background light intensities, the Ca 2 § modulation of the guanylate cyclase appears to be the most important for sensitivity regulation. At higher light intensities, especially above half-saturation of the response, the Ca 2 § modulation of the light-stimulated phosphodiesterase shows a progressively important influence on the light response; it also extends the Weber-Fechner behavior of the cell to higher intensities. The contribution of the Ca 2+ modulation of the cGMP-gated channel is slight throughout.

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Section: Phosphodiesterase Activity and Ca "2+ Dependencesupporting

confidence: 74%

The cGMP-phosphodiesterase and its contribution to sensitivity regulation in retinal rods

Koutalos

Nakatani

Yau

1995

The Journal of General Physiology

108

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“…The light-activated rate is assumed to increase proportionally with the photon content I v of a flash. For the light intensities we are considering in this paper (< 104 photoisomerizations s-~), this seems to be a reasonable assumption judging from biochemical measurements (Barkdoll et al, 1989; see also Discussion). Substituting Eqs.…”

Section: Appendixsupporting

confidence: 51%

Calcium feedback and sensitivity regulation in primate rods.

Tamura

Nakatani

Yau

1991

The Journal of General Physiology

125

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Membrane current was recorded from a single primate rod with a suction pipette while the cell was bath perfused with solutions maintained at a temperature of ~ 38°C. A transient inward current was observed at the onset of bright illumination after briefly exposing the outer segment in darkness to Ringer's (Locke) solution containing 3-isobutyl-l-methylxanthine (IBMX), an inhibitor of cGMP phosphodiesterase. After briefly removing external Na ÷ from around the outer segment in darkness, a similar current was observed upon Na + restoration in bright light. By analogy to amphibian rods, this inward current was interpreted to represent the activity of an electrogenic Na÷-dependent Ca 2+ efl]ux, which under physiological conditions in the light is expected to reduce the free Ca 2+ in the outer segment and provide negative feedback (the "Ca 2+ feedback") to the phototransduction process. The exchange current had a saturated amplitude of up to ~ 5 pA and a decline time course that appeared to have more than one exponential component. In the absence of the Ca 2+ feedback, made possible by removing the Ca 2÷ influx and efflux at the outer segment using a 0 Na+-0 Ca 2+ external solution, the response of a rod to a dim flash was two to three times larger and had a longer time to peak than in physiological solution. These changes can be approximately accounted for by a simple model describing the Ca 2÷ feedback in primate rods. The dark hydrolytic rate for cGMP was estimated to be 1.2 s -~. The incremental hydrolytic rate, [3*(t), activated by one photoisomerization was ~0.09 s -~ at its peak, with a time-integrated activity, ff3*(t)dt, of ~ 0.033, both numbers being derived assuming spatial homogeneity in the outer segment. Finally, we have found that primate rods adapt to light in much the same way as amphibian and other mammalian rods, such as showing a Weber-Fechner relation between flash sensitivity and background light. The Ca 2÷ feedback model we have constructed can also explain this feature reasonably well.

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“…The phosphodiesterase activity is only influenced by calcium at unphysiologically high concentrations (i.e. 0.1 mM, Barkdoll et al, 1989). An effect of calcium on the lifetime of one or more components of the transduction cascade was discussed by Torre et al (1986), but until now the biochemical data are not sufficient to decide whether this influence of calcium occurs in vivo.…”

Section: Discussionmentioning

confidence: 99%

A 26 kd calcium binding protein from bovine rod outer segments as modulator of photoreceptor guanylate cyclase.

1991

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The resynthesis of cGMP in vertebrate photoreceptors by guanylate cyclase is one of the key events leading to the reopening of cGMP‐gated channels after photoexcitation. Guanylate cyclase activity in vertebrate rod outer segments is dependent on the free calcium concentration. The basal activity of the enzyme observed at high concentrations of free calcium (greater than 0.5 microM) increases when the free calcium concentration is lowered into the nanomolar range (less than 0.1 microM). This effect of calcium is known to be mediated by a soluble calcium‐sensitive protein in a highly cooperative way. We here show that this soluble protein, i.e. the modulator of photoreceptor guanylate cyclase, is a 26 kd protein. Reconstitution of the purified 26 kd protein with washed rod outer segment membranes containing guanylate cyclase revealed a 3‐ to 4‐fold increase of cyclase activity when the free calcium concentration was lowered in the physiological range from 0.5 microM to 4 nM. Guanylate cyclase in whole rod outer segments was stimulated 10‐fold in the same calcium range. The activation process in the reconstituted system was similar to the one in the native rod outer segment preparation, it showed a high cooperativity with a Hill coefficient n between 1.4 and 3.5. The half‐maximal activation occurred between 110 and 220 nM free calcium. The molar ratio of the modulator to rhodopsin is 1:76 +/‐ 32. The protein is a calcium binding protein as detected with 45Ca autoradiography. Partial amino acid sequence analysis revealed a 60% homology to visinin from chicken cones.

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Calcium dependence of the activation and inactivation kinetics of the light-activated phosphodiesterase of retinal rods.

Cited by 36 publications

References 42 publications

The cGMP-phosphodiesterase and its contribution to sensitivity regulation in retinal rods

The cGMP-phosphodiesterase and its contribution to sensitivity regulation in retinal rods

Calcium feedback and sensitivity regulation in primate rods.

A 26 kd calcium binding protein from bovine rod outer segments as modulator of photoreceptor guanylate cyclase.

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