scholarly journals Developmental regulation of calcium-dependent feedback in Xenopus rods

2004 ◽  
Vol 124 (5) ◽  
pp. 569-585 ◽  
Author(s):  
Eduardo Solessio ◽  
Shobana S. Mani ◽  
Nicolas Cuenca ◽  
Gustav A. Engbretson ◽  
Robert B. Barlow ◽  
...  
Keyword(s):  
Guanylate Cyclase ◽  
Single Photon ◽  
Developmental Regulation ◽  
Cutoff Frequency ◽  
Power Spectra ◽  
Recovery Phase ◽  
Calcium Dependent ◽  
Time To Peak ◽  
Single Photon Response ◽  
Phototransduction Pathway

The kinetics of activation and inactivation in the phototransduction pathway of developing Xenopus rods were studied. The gain of the activation steps in transduction (amplification) increased and photoresponses became more rapid as the rods matured from the larval to the adult stage. The time to peak was significantly shorter in adults (1.3 s) than tadpoles (2 s). Moreover, adult rods recovered twice as fast from saturating flashes than did larval rods without changes of the dominant time constant (2.5 s). Guanylate cyclase (GC) activity, determined using IBMX steps, increased in adult rods from ∼1.1 s−1 to 3.7 s−1 5 s after a saturating flash delivering 6,000 photoisomerizations. In larval rods, it increased from 1.8 s−1 to 4.0 s−1 9 s after an equivalent flash. However, the ratio of amplification to the measured dark phosphodiesterase activity was constant. Guanylate cyclase–activating protein (GCAP1) levels and normalized Na+/Ca2+, K+ exchanger currents were increased in adults compared with tadpoles. Together, these results are consistent with the acceleration of the recovery phase in adult rods via developmental regulation of calcium homeostasis. Despite these large changes, the single photon response amplitude was ∼0.6 pA throughout development. Reduction of calcium feedback with BAPTA increased adult single photon response amplitudes threefold and reduced its cutoff frequency to that observed with tadpole rods. Linear mathematical modeling suggests that calcium-dependent feedback can account for the observed differences in the power spectra of larval and adult rods. We conclude that larval Xenopus maximize sensitivity at the expense of slower response kinetics while adults maximize response kinetics at the expense of sensitivity.

scholarly journals Nano-optical single-photon response mapping of waveguide integrated molybdenum silicide (MoSi) superconducting nanowires

2016 ◽  
Vol 24 (13) ◽  
pp. 13931 ◽  
Author(s):  
Jian Li ◽  
Robert A. Kirkwood ◽  
Luke J. Baker ◽  
David Bosworth ◽  
Kleanthis Erotokritou ◽  
...  
Keyword(s):  
Single Photon ◽  
Molybdenum Silicide ◽  
Superconducting Nanowires ◽  
Response Mapping ◽  
Single Photon Response

scholarly journals Diffusion of the Second Messengers in the Cytoplasm Acts as a Variability Suppressor of the Single Photon Response in Vertebrate Phototransduction

2008 ◽  
Vol 94 (9) ◽  
pp. 3363-3383 ◽  
Author(s):  
Paolo Bisegna ◽  
Giovanni Caruso ◽  
Daniele Andreucci ◽  
Lixin Shen ◽  
Vsevolod V. Gurevich ◽  
...  
Keyword(s):  
Single Photon ◽  
Second Messengers ◽  
Single Photon Response

Properties of channels mediating the apamin-insensitive afterhyperpolarization in vagal motoneurons

1995 ◽  
Vol 74 (4) ◽  
pp. 1772-1776 ◽  
Author(s):  
P. Sah
Keyword(s):  
Single Channel ◽  
Slow Component ◽  
Power Spectra ◽  
Corner Frequency ◽  
Equilibrium Potential ◽  
Fluctuation Analysis ◽  
Motor Nucleus ◽  
Small Current ◽  
Calcium Dependent ◽  
Dorsal Motor Nucleus

1. Whole cell recordings were obtained from neurons of the dorsal motor nucleus of the vagus in transverse slices of guinea pig medulla. From a holding potential of -40 mV, short depolarizing voltage steps activated two calcium-dependent potassium currents, Gk(Ca),1 and Gk(Ca),2. 2. Gk(Ca),1 was completely blocked by apamin (100 nM). Gk(Ca),2 was apamin insensitive, voltage independent, and reversed close to the potassium equilibrium potential. 3. Activation of Gk(Ca),2 was associated with an increase in current variance. The channels underlying the slow component were analyzed by stationary and nonstationary fluctuation analysis. Current variance was linearly related to mean current for small current amplitudes but clearly deviated from linearity near the peak of Gk(Ca),2. The predicted single channel conductance was 6.8 +/- 2.5 (SE) pS. Probability of channel opening rose to at most 0.68. The average number of available Gk(Ca),2 channels on vagal neurons was 4,437 +/- 591. 4. Power spectra were constructed from the peak current. Spectra were well fitted with a single Lorentzian with a corner frequency of 72 +/- 7 Hz. The mean burst duration of the channels was 3.8 +/- 0.5 ms. These results indicate that a new type of calcium-activated channel underlies Gk(Ca),2.

scholarly journals Analytical Study of Front-End Circuits Coupled to Silicon Photomultipliers for Timing Performance Estimation under the Influence of Parasitic Components

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4428
Author(s):  
Pietro Antonio Paolo Calò ◽  
Savino Petrignani ◽  
Michele Di Gioia ◽  
Cristoforo Marzocca
Keyword(s):  
Single Photon ◽  
Performance Estimation ◽  
Laser Source ◽  
Detector Response ◽  
Silicon Photomultipliers ◽  
Parasitic Inductance ◽  
Front End ◽  
Single Photon Response ◽  
Variable Configuration ◽  
Definition Of

Full exploitation of the intrinsic fast timing capabilities of analog silicon photomultipliers (SiPMs) requires suitable front-end electronics. Even a parasitic inductance of a few nH, associated to the interconnections between the SiPM and the preamplifier, can significantly degrade the steepness of the detector response, thus compromising the timing accuracy. In this work, we propose a simple analytic expression for the single-photon response of a SiPM coupled to the front-end electronics, as a function of the main parameters of the detector and the preamplifier, taking into account the parasitic inductance. The model is useful to evaluate the influence of each parameter of the system on the slope of its response and to guide the designer in the definition of the architecture and the specifications for the front-end electronics. The results provided by the model have been successfully compared with experimental measurements from a front-end circuit with variable configuration based on a bipolar junction transistor (BJT), coupled to a 3 × 3 mm2 SiPM stimulated by a fast-pulsed laser source.

A novel calcium-dependent activator of retinal rod outer segment membrane guanylate cyclase

Biochemistry ◽  
1995 ◽  
Vol 34 (44) ◽  
pp. 14279-14283 ◽  
Author(s):  
Nikolay Pozdnyakov ◽  
Akiko Yoshida ◽  
Nigel G. F. Cooper ◽  
Alexander Margulis ◽  
Teresa Duda ◽  
...  
Keyword(s):  
Guanylate Cyclase ◽  
Outer Segment ◽  
Membrane Guanylate Cyclase ◽  
Rod Outer Segment ◽  
Calcium Dependent ◽  
Retinal Rod

scholarly journals Method For Measuring Sub-Micron Facula At Single-Photon Level With Silicon Photomultiplier

2021 ◽  
Author(s):  
Yaxian Yang ◽  
Guoqing Zhang ◽  
Chen Zhang ◽  
Xinyue Cao ◽  
Lina Liu ◽  
...  
Keyword(s):  
Single Photon ◽  
Dimensional Space ◽  
Avalanche Photodiode ◽  
Objective Lens ◽  
Silicon Photomultiplier ◽  
Silicon Photomultipliers ◽  
Positioning Stage ◽  
Weak Light ◽  
Single Photon Response ◽  
Nominal Resolution

Abstract Sub-micron faculae (light spots) at the single-photon level have important applications in many fields. This report demonstrates a method for measuring facula size at the sub-micron single-photon level indirectly. The developed method utilizes Silicon Photomultipliers (SiPMs) as the single-photon response detectors, combined with a nano-positioning stage. The approach involves one- or two-dimensional space scanning and a deconvolution operation, which enable evaluations of the size and spatial distribution of focused facula in a single-photon-level pulsed laser. The results indicate that the average full width at half maximum of the faculae is about 0.66 µm, which is close to the nominal resolution of the objective lens of the microscope (0.42 µm). The proposed method has two key advantages: (1) it can measure sub-micron facula at the single-photon level, and (2) the sub-micron facula can easily be aligned with the detector because the array area of the avalanche photodiode cells in SiPM is usually larger than one square millimeter, and there is no need to put an optical slit, knife edge, or pinhole in front of the detector. The method described herein is applicable in weak light facula detection related fields.

Circadian Modulation of Temporal Properties of the Rod Pathway in Larval Xenopus

2004 ◽  
Vol 92 (5) ◽  
pp. 2672-2684 ◽  
Author(s):  
Eduardo Solessio ◽  
David Scheraga ◽  
Gustav A. Engbretson ◽  
Barry E. Knox ◽  
Robert B. Barlow
Keyword(s):  
Single Photon ◽  
Night Shift ◽  
Cutoff Frequency ◽  
Visual Sensitivity ◽  
Circadian Clocks ◽  
Constant Darkness ◽  
Diurnal Changes ◽  
Single Photon Detection ◽  
Temporal Properties ◽  
Endogenous Circadian Rhythm

Circadian clocks are integral components of visual systems. They help adjust an animal's vision to diurnal changes in ambient illumination. To understand how circadian clocks may adapt visual sensitivity, we investigated the spatial and temporal properties of optomotor responses of young Xenopus laevis tadpoles (Nieuwkoop and Faber, developmental stage 48) using a modified 2-alternative preferential-viewing method. We maintained animals in constant darkness and measured temporal sensitivity during their subjective day and night. We found that their behavioral responses can be explained in terms of 2 mechanisms with different temporal properties. The more sensitive mechanism operates at low temporal frequencies and intermediate wavelengths (λmax = 520 nm), properties consistent with rod signals. Threshold for this mechanism is approximately 0.04 photoisomerizations rod−1 s−1, consistent with single-photon detection. A less-sensitive mechanism responds to higher temporal frequencies (cutoff = 12 Hz) and has broad spectral sensitivity (370–720 nm), consistent with multiple classes of cone signals. This cone mechanism does not change, but the cutoff frequency of the more sensitive rod mechanism shifts from 0.35 Hz at night to 1.1 Hz during the subjective day, thereby enhancing the animal's sensitivity to dim rapidly changing stimuli. This day–night shift in rod temporal cutoff frequency cycles in complete darkness, characteristic of an endogenous circadian rhythm. The temporal properties of the behaviorally measured rod mechanism correspond closely with those of the electrophysiologically measured retinal response, indicating that the rod signals are modulated at the level of the outer retina.

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