Characterization of Guanylate cyclase of rod outer segments of the bovine retina

Krishnan, N.; Fletcher, Reid; Chader, Gerald J.; Krishina, G.

doi:10.1016/0005-2744(78)90053-0

Cited by 65 publications

(33 citation statements)

References 25 publications

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“…The 308 IONIC MO VEMENTS IN RODS efficacy sequence for divalent cations in a nominally Na+-Ca2+-Mg2+-free solution containing 0-5 mM-IBMX, is: Mn2+ > Ba2+> (Ca2+, Co2+, Mg2+, Sr2+). This sequence is the same as the activation sequence for guanylate cyclase in vertebrate rods (Krishnan, Fletcher, Chader & Krishna, 1978) suggesting a possible dependence of selectivity also on guanosine-3' : 5'-cyclic monophosphate metabolism.…”

Section: The Selectivity Of the Light-sensitive Channelmentioning

confidence: 63%

Ionic movements through light‐sensitive channels of toad rods.

Capovilla¹,

Caretta²,

Cervetto³

et al. 1983

The Journal of Physiology

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SUMMARY1. Electrical photoresponses of rods in the isolated toad retina were recorded during ionic manipulations of the Na+-free extracellular medium.2. In the presence of a concentration of external Ca2+ above 10-5 M, voltage photoresponses were observed only in the presence of external Na+ or Li+.3. When external Ca2+ was reduced below 10-6 M, voltage photoresponses of normal polarity could be detected even in the absence of Na+ or Li+, but in the presence of external Mg2+.4. In the presence of normal extracellular Ca2+ hyperpolarizing photoresponses were observed even in the absence of Na+ or Li+, provided small amounts of phosphodiesterase inhibitors (IBMX, RO 20-1724, papaverine, caffeine, theophylline) were added to the perfusate.5. Responses obtained in low-Na+ IBMX solutions required the presence of millimolar amounts of a variety ofdivalent cations, among which Mn2+ and Ba2+ were the most effective.6. When the concentration of both external Ca2+ and Mg2+ was reduced to micromolar amounts, depolarizing photoresponses were observed. In these conditions measurements with radioactive tracers showed a light-modulated efflux of 42K+ or 86Rb+.7. The light-modulated 42K+ or 86Rb+ efflux was halved by 2-6 mM-external K+ and was completely blocked when K+ was raised above 10 mM.8. These results show that ionic movements through light-sensitive channels are controlled by Ca2+ and Mg2+ and possibly also be the intracellular level of cyclic nucleotides. Moreover, the movement of ions through the light-sensitive channel, does not obey the independence principle.

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Section: The Selectivity Of the Light-sensitive Channelmentioning

confidence: 63%

Ionic movements through light‐sensitive channels of toad rods.

Capovilla¹,

Caretta²,

Cervetto³

et al. 1983

The Journal of Physiology

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“…But in the experiments supporting this view the solution changes were not fast enough to separate possible external and internal effects of divalent cations. For instance in rods treated with 0 5 mM-IBMX, Mn2+ appeared the most permeant cation, but since Mn2+ is known to be a potent activator of the cyclase (Krishnan, Fletcher, Chader & Krishna, 1978) it was difficult to separate direct effects on the channel from metabolic effects on cytoplasmic proteins. In the experiments shown in Figs 1 and 2 the slow activation of the photocurrent can be ascribed to the development of the IBMX effects or to more complex events in which the entry of divalent cations is affecting the cyclase or the phosphodiesterase.…”

Section: Resultsmentioning

confidence: 99%

The modulation of the ionic selectivity of the light‐sensitive current in isolated rods of the tiger salamander.

Cervetto

Menini

Rispoli

et al. 1988

The Journal of Physiology

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SUMMARY1. By using the method of Hodgkin, McNaughton & Nunn (1985) for rapidly changing the extracellular medium, we analysed the effect of the organic compound IBMX (3-isobutyl-1-methylxanthine) on the movement of divalent cations through the light-sensitive channels of isolated retinal rods of the tiger salamander. (Menini, Rispoli & Torre, 1988). 5. When the rod is pre-treated with an extracellular solution containing 0 5 mM-IBMX the half-activation of the photocurrent which can be carried by Mg2+, Ba2+ and Sr2+ is equivalent to or greater than 10 mm. In the absence of pre-treatment with IBMX the half-activation of the photocurrent carried by Mg2+, Ba2+ and Sr2+ is less than 5 mm.6. We conclude that the light-sensitive channel can exist in at least two distinct open states. The selectivity of the channel in the first open state is as described in a previous paper (Menini et al.

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“…Unlike the other particulate guanylate cyclase, rod outer segment guanylate cyclase is not solubilized by detergent treatment and is not activated by sodium azide (31,46) . In this study, 1 mM sodium azide had no effect on the reaction products, which is in agreement with the biochemical evidence.…”

Section: Discussionmentioning

confidence: 99%

“…Light or dark or some other accompanying factor, for example a calcium ion or other divalent metal ion (21), may affect the regulating site of guanylate cyclase. It is also possible that ion mobilization or ATP concentration may affect the guanylate cyclase activity (31).…”

Section: Discussionmentioning

confidence: 99%