Measurement of the intracellular free calcium concentration in salamander rods

McNaughton, Peter A.; Cervetto, Luigi; Nunn, B J

doi:10.1038/322261a0

Cited by 175 publications

(112 citation statements)

References 13 publications

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“…Since Ca2+ levels in ROSs reflect recent light signaling, and neuronal adenylyl cyclase is commonly regulated by Ca2+/calmodulin, the possibility that ROS adenylyl cyclase might be regulated by Ca2+ was tested. In bovine ROS preparations in which soluble components are retained, adenylyl cyclase activity exhibited a striking dependence on free [Ca2+] over its physiological range (7,(23)(24)(25) in ROS cytosol (Fig. 2).…”

Section: Methodsmentioning

confidence: 99%

Regulation of phosducin phosphorylation in retinal rods by Ca2+/calmodulin-dependent adenylyl cyclase.

Willardson

Wilkins

Yoshida

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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The phosphoprotein phosducin (Pd) regulates many guanine nucleotide binding protein (G protein)-linked signaling pathways. In visual signal transduction, unphosphorylated Pd blocks the interaction of light-activated rhodopsin with its G protein (Gt) by binding to the fry subunits of Gt and preventing their association with the Gta subunit. When Pd is phosphorylated by cAMP-dependent protein kinase, it no longer inhibits Gt subunit interactions.Thus, factors that determine the phosphorylation state of Pd in rod outer segments are important in controlling the number of Gts available for activation by rhodopsin. The cyclic nucleotide dependencies of the rate of Pd phosphorylation by endogenous cAMP-dependent protein kinase suggest that cAMP, and not cGMP, controls Pd phosphorylation. The synthesis of cAMP by adenylyl cyclase in rod outer segment preparations was found to be dependent on Ca2+ and calmodulin. The Ca2+ dependence was within the physiological range of Ca2+ concentrations in rods (K./2 = 230 + 9 nM) and was highly cooperative (napp = 3.6 + 0.5). Through its effect on adenylyl cyclase and cAMP-dependent protein kinase, physiologically high Ca2+ (1100 nM) was found to increase the rate of Pd phosphorylation 3-fold compared to the rate of phosphorylation at physiologically low Ca2+ (8 nM). No evidence for Pd phosphorylation by other Ca2+-dependent kinases was found. These results suggest that Ca2+ can regulate the light response at the level of Gt activation through its effect on the phosphorylation state of Pd.

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Section: Methodsmentioning

confidence: 99%

Regulation of phosducin phosphorylation in retinal rods by Ca2+/calmodulin-dependent adenylyl cyclase.

Willardson

Wilkins

Yoshida

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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“…2) has been demonstrated to be due to the operation of an electrogenic Na+-Ca2+, K+ exchange which reduces [Ca2+]i after a bright flash (Yau & Nakatani, 1985; McNaughton, Cervetto & Nunn, 1986;Hodgkin, MeNaughton & Nunn 1987;Tamura, Nakatani & Yau, 1991). Temperature (0C) Fig.…”

Section: Basic Observationsmentioning

confidence: 99%

Temperature dependence of the light response in rat rods.

Robinson

Ratto

Lagnado

et al. 1993

The Journal of Physiology

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SUMMARY1. The effects of temperature on the light responses of rat rods have been investigated over the range 17-40 'C.2. The amplitude of the light-sensitive current increased with temperature with a mean temperature coefficient (Qlo) of 2 47.3. The amplitude of the Na'-Ca2+, K+ exchange current decreased with temperature when expressed as a fraction of the light-sensitive current, showing that the light-sensitive channel becomes less permeable to calcium as the temperature is raised. The time constant of relaxation of the exchange current was little affected by temperature.4. The flash intensity required to give a half-saturating response increased with temperature with a mean Q1o of 168.5. The responses to single photoisomerizations were determined from amplitude histograms of the responses to dim-flash trains. The amplitude of the response to a single photoisomerization decreased with temperature when expressed as a fraction of the light-sensitive current, but the change was not sufficient to account for the overall decrease in sensitivity.6. The fraction of dim flashes that produced a photoisomerization decreased with temperature. This decrease in photon capture efficiency together with the decrease in the relative size of the single photon event fully accounts for the observed change in sensitivity.7. The speed of the falling phase of the dim-flash response was accelerated more by warming than the rising phase, and it was therefore not possible to superimpose light responses at different temperatures by a simple change in time scale.

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“…Ca ~+ entry in the dark provides negative feedback control of cGMP synthesis (LoUey and Racz, 1982;Pepe, Panfoli, and Cugnoli, 1986;Hodgkin and Nunn, 1988;Koch and Stryer, 1988;Dizhoor, Ray, Kumar, Niemi, Spencer, Brolley, Walsh, Philipov, Hurley, and Stryer, 1991). A light-induced drop in internal Ca 2+ concentration (Yau and Nakatani, 1985;McNaughton, Cervetto, and Nunn, 1986) is important for the recovery of the light response and for light adaptation (Matthews, Murphy, Fain, and Lamb, 1988;Nakatani and Yau, 1988b).…”

Section: Introductionmentioning

confidence: 99%

Interactions between divalent cations and the gating machinery of cyclic GMP-activated channels in salamander retinal rods.

Karpen

Brown

Stryer

et al. 1993

The Journal of General Physiology

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The effects of divalent cations on the gating of the cGMP-activated channel, and the effects of gating on the movement of divalent cations in and out of the channel's pore were studied by recording macroscopic currents in excised membrane patches from salamander retinal rods. The fractional block of cGMPactivated Na + currents by internal and external Mg 2+ as well as internal Ca ~+ was nearly independent ofcGMP concentration. This indicates that Mg 2÷ and Ca ~÷ bind with similar affinity to open and closed states of the channel. In contrast, the efficiency of block by internal Cd 2÷ or Zn 2÷ increased in proportion to the fraction of open channels, indicating that these ions preferentially occupy open channels. The kinetics of block by internal Ni 2+, which competes with Mg z÷ but blocks more slowly, were found to be unaffected by the fraction of channels open. External Ni z÷, however, blocked and unblocked much more rapidly when channels were mostly open. This suggests that within the pore a gate is located between the binding site(s) for ions and the extraceUular mouth of the channel. Micromolar concentrations of the transition metal divalent cations Ni 2÷, Cd 2+, Zn ~+, and Mn 2÷ applied to the cytoplasmic surface of a patch potentiated the response to subsaturating concentrations of cGMP without affecting the maximum current induced by saturating cGMP. The concentration of cGMP that opened half the channels was often lowered by a factor of three or more. Potentiation persisted after the experimental chamber was washed with divalent-free solution and fresh cGMP was applied, indicating that it does not result from an interaction between divalent cations and cGMP in solution; 1 mM EDTA or isotonic MgCl~ reversed potentiation. Voltage-jump experiments suggest that potentiation results from an increase in the rate of cGMP binding. Lowering the ionic strength of the bathing solution enhanced potentiation, suggesting that it involves electrostatic interactions. The strong electrostatic effect on cGMP binding and absence of effect on ion permeation through open channels implies that the cGMP binding sites on the channel are well separated from the permeation pathway.Address reprint requests to Dr.

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Measurement of the intracellular free calcium concentration in salamander rods

Cited by 175 publications

References 13 publications

Regulation of phosducin phosphorylation in retinal rods by Ca2+/calmodulin-dependent adenylyl cyclase.

Regulation of phosducin phosphorylation in retinal rods by Ca2+/calmodulin-dependent adenylyl cyclase.

Temperature dependence of the light response in rat rods.

Interactions between divalent cations and the gating machinery of cyclic GMP-activated channels in salamander retinal rods.

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