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

Cervetto, Luigi; Menini, Anna; Rispoli, Giorgio; Torre, Vincent

doi:10.1113/jphysiol.1988.sp017375

Cited by 33 publications

(20 citation statements)

References 30 publications

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“…However, subsequent studies showed that by altering surface charge, a lowered [Ca 2+ ] o causes a leftward (negative) shift in I Ca activation that paradoxically promotes Ca 2+ influx into the synaptic terminals of photoreceptor cells, even in the presence of divalent cations used to block I Ca (Piccolino et al, 1996(Piccolino et al, , 1999Cadetti et al, 2004). Lowering [Ca 2+ ] o also enhances the amplitude of photoreceptor light responses (Bertrand et al, 1978;Cervetto et al, 1988). The combined effects of low divalent cation solutions on photoreceptor light responses and membrane surface charge are sufficient to account for the persistence of horizontal and bipolar cell light responses (Cadetti et al, 2004).…”

Section: Is There Calcium-independent Transmission At Ribbon Synapses?mentioning

confidence: 99%

Synaptic transmission at retinal ribbon synapses

Heidelberger

Thoreson

Witkovsky

2005

Progress in Retinal and Eye Research

209

231

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The molecular organization of ribbon synapses in photoreceptors and ON bipolar cells is reviewed in relation to the process of neurotransmitter release. The interactions between ribbon synapseassociated proteins, synaptic vesicle fusion machinery and the voltage-gated calcium channels that gate transmitter release at ribbon synapses are discussed in relation to the process of synaptic vesicle exocytosis. We describe structural and mechanistic specializations that permit the ON bipolar cell to release transmitter at a much higher rate than the photoreceptor does, under in vivo conditions. We also consider the modulation of exocytosis at photoreceptor synapses, with an emphasis on the regulation of calcium channels.

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Section: Is There Calcium-independent Transmission At Ribbon Synapses?mentioning

confidence: 99%

Synaptic transmission at retinal ribbon synapses

Heidelberger

Thoreson

Witkovsky

2005

Progress in Retinal and Eye Research

209

231

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“…The selectivity of this channel to monovalent and divalent cations and their interaction has been studied in intact rods by changing solutions at the extracellular side of the cell (Yau & Nakatani, 1984;Hodgkin, McNaughton & Nunn, 1985;Nakatani & Yau, 1988a;. On the basis of results of experiments performed in intact cells Cervetto, Menini, Rispoli & Torre (1988) have suggested that the level of cyclic GMP can modulate the permeation properties of divalent cations through the light-sensitive channel: an elevation of intracellular cyclic GMP appeared to decrease the affinity of a divalent cation for the channel. However, the study of ion selectivity in intact cells is complicated by the fact that intracellular concentration of divalent cations and of cyclic GMP cannot be controlled.…”

Section: Introductionmentioning

confidence: 99%

Blockage and permeation of divalent cations through the cyclic GMP‐activated channel from tiger salamander retinal rods.

Colamartino

Menini

Torre

1991

The Journal of Physiology

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SUMMARY1. Blockage and permeation of divalent cations through channels activated by guanosine 3',5'-cyclic monophosphate (cyclic GMP) were studied in membrane patches excised from retinal rods of the tiger salamander Ambystoma tigrinum by rapidly changing the ionic medium bathing the intracellular side of the excised membrane.2. The Na+ current, observed when 110 mm-NaCl was present on both sides of the membrane patch, was reduced by the addition of 1 mm of the chloride salts of Ca2+, Mg2+, Sr2+, Ba2+ or Mn2+ to the bathing medium. The sequence of blocking potency at + 60 mV was Mg2+ > Mn2+ -Ba2+ > Ca2+ > Sr2+, while at -60 mV it was Ba2+ > Ca2+ > Sr2+ > Mn2+ _ Mg2+. For all divalent cations the blocking effect depended, in a complex way, on the membrane potential.3. The blocking effect of Ca2+ and Mg2+ increased when the concentration of cyclic GMP was reduced from 100 to 5 ,UM. At -60 mV 1 mM-Ca2+ blocked about 34 % of the Na+ current in the presence of 100 #uM-cyclic GMP, while in the presence of 5/tMcyclic GMP, 1 mM-Ca2+ blocked about 56% of the Na+ current.4. When, in the presence of 100 gm-cyclic GMP, 110 G. COLAMARTINO, A. MENINI AND V. TORRE 7. The concentration of cyclic GMP activating half of the maximal current carried by Mg2L was about 85 JtM. No Mg2" current was observed in the presence of less than 20 1uM-cyclic GMP. A good fit of the experimental data on the dependence of the Mg2+ current upon the concentration of cyclic GMP can be obtained by assuming that the permeation of Mg2+ through the channel requires the binding of three to five molecules of cyclic GMP.8. These results show that blockage and permeation of divalent cations depend on the level of cyclic GMP in a complex way. The permeation sequence of divalent cations through the cyclic GMP-gated channel in excised patches is similar to but not identical to the selectivity sequence of divalent cations through the channel in intact rods.

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“…Bertrand et al, 1978;Cervetto et al, 1988;Piccolino et al, , 1998. Lowering [Ca 2+ ] o causes a decrease in [Ca] i through the action of the Na + /Ca 2+ exchanger (Cervetto et al, 1988;Rispoli et al, 1996;McNaughton, 1991) and this reduction in [Ca 2+ ] i promotes the opening of cGMP-gated cation channels in the outer segment (Koch and Stryer, 1998;Hsu and Molday, 1993;Ebrey and Koutalos, 2001). This sequence of events can account for the depolarization and increase in the amplitude of the light response observed after lowering extracellular Ca 2+ .…”

Section: Discussionmentioning

confidence: 99%

“…As shown in Fig. 7A, lowering extracellular Ca 2+ more often produced a strong membrane potential depolarization and a large increase in the amplitude of the light response (see also Bertrand et al, 1978;Cervetto et al, 1988;Piccolino et al, ,1998.…”

Section: Inverted Light Responsesmentioning

confidence: 99%

“…A second factor that complicated interpretation of earlier experiments arises from the fact that lowering extracellular Ca 2+ causes photoreceptors to depolarize and enhances their light responses (Bertrand et al, 1978;Cervetto et al, 1988;Piccolino et al, , 1998. Thus, independent of their actions on synaptic transmission, effects of low Ca 2+ solutions on presynaptic membrane potential and light response amplitude can also contribute to the persistence of HC light responses.…”

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confidence: 99%

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Pre- and post-synaptic effects of manipulating surface charge with divalent cations at the photoreceptor synapse

2004

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Persistence of horizontal cell (HC) light responses in extracellular solutions containing low Ca 2+ plus divalent cations to block Ca 2+ currents (I Ca ) has been attributed to Ca 2+ -independent neurotransmission. Using a retinal slice preparation to record both I Ca To bypass light stimulation, OFF bipolar cells were stimulated by steps to −40 mV applied to presynaptic rods during simultaneous paired recordings. Consistent with surface charge theory, the post-synaptic current was inhibited by Zn 2+ and this inhibition was relieved by lowering [Ca 2+ ] o . Nominally divalent-free media produced inversion of HC light responses even though rod light responses remained hyperpolarizing; HC response inversion can be explained by surface chargemediated shifts in I Ca . In summary, HC light responses modifications induced by low divalent cation solutions can be explained by effects on photoreceptor light responses and membrane surface charge without necessitating Ca 2+ -independent neurotransmission. Furthermore, these results suggest that surface charge effects accompanying physiological changing divalent cation levels in the synaptic cleft may provide a means for modulating synaptic output from photoreceptors.

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

Cited by 33 publications

References 30 publications

Synaptic transmission at retinal ribbon synapses

Synaptic transmission at retinal ribbon synapses

Blockage and permeation of divalent cations through the cyclic GMP‐activated channel from tiger salamander retinal rods.

Pre- and post-synaptic effects of manipulating surface charge with divalent cations at the photoreceptor synapse

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