The role of cytoplasmic calcium in photoreceptor light adaptation

1992 ◽  
Vol 86 (1-3) ◽  
pp. 147-155
Author(s):  
HR Matthews
Keyword(s):  
Light Adaptation ◽  
Cytoplasmic Calcium

Light adaptation and color opponency of horizontal cells in the turtle retina

2003 ◽  
Vol 20 (4) ◽  
pp. 437-452 ◽  
Author(s):  
GILAD TWIG ◽  
HANNA LEVY ◽  
ELITE WEINER ◽  
IDO PERLMAN
Keyword(s):  
Light Adaptation ◽  
Light Sensitivity ◽  
Horizontal Cells ◽  
Background Illumination ◽  
Voltage Range ◽  
Background Adaptation ◽  
Color Opponency ◽  
Light Stimuli ◽  
Type C

Chromaticity-type (C-type) horizontal cells of the turtle retina receive antagonistic inputs from cones of different spectral types, and therefore their response to background illumination is expected to reflect light adaptation of the cones and the interactions between their antagonistic inputs. Our goal was to study the behavior of C-type horizontal cells during background illumination and to evaluate the role of wavelength in background adaptation. The photoresponses of C-type horizontal cells were recorded intracellularly in the everted eyecup preparation of the turtleMauremys caspicaduring chromatic background illuminations. The voltage range of operation was either reduced or augmented, depending upon the wavelengths of the background and of the light stimuli, while the sensitivity to light was decreased by any background. The response–intensity curves were shifted to brighter intensities and became steeper as the background lights were made brighter regardless of wavelength. Comparing the effects of cone iso-luminant backgrounds on the Red/Green C-type horizontal cells indicated that background desensitization in these cells could not solely reflect background adaptation of cones but also depend upon response compression/expansion and changes in synaptic transmission. This leads to wavelength dependency of background adaptation in C-type horizontal cells, that is expressed as increased light sensitivity (smaller threshold elevation) and improved suprathreshold contrast detection when the wavelengths of the background and light stimuli were chosen to exert opponent effects on membrane potential.

Albumin modulation of capillary permeability: role of endothelial cell [Ca2+]i

1993 ◽  
Vol 265 (1) ◽  
pp. H74-H82 ◽  
Author(s):  
P. He ◽  
F. E. Curry
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Calcium Concentration ◽  
Capillary Permeability ◽  
Common Mechanism ◽  
Cytoplasmic Calcium ◽  
Adsorption Model ◽  
Endothelial Cell Surface ◽  
Mesenteric Microvessels

Albumin is required in vascular perfusates to maintain the normal permeability of microvessel walls. The most common mechanism proposed for action of albumin involves binding to the endothelial cell surface to increase the resistance to water and solute flows through hydraulic pathways across the capillary wall. The results of the present experiments do not conform to this simple adsorption model. Ringer perfusion increased the hydraulic conductivity (Lp) of the wall of single perfused frog mesenteric microvessels by 4.0 +/- 0.5-fold. The increase in Lp was associated with an increase of cytoplasmic calcium concentration ([Ca2+]i) from 59 +/- 5 nM when albumin was in the perfusate to a transient peak of 181 +/- 13 nM, 1–2 min after Ringer perfusion. [Ca2+]i then fell back to close to 100 nM. Processes that reduced Ca2+ influx into endothelial cells (removal of extracellular Ca2+, membrane depolarization) reduced Ca2+ influx and attenuated the increase in [Ca2+]i. The same processes abolished the increase in Lp after Ringer perfusion and restored Lp to close to control values during Ringer perfusion. Thus Ca2+ entry into endothelial cells is required to initiate and maintain the increased permeability during Ringer perfusion.

The role of cytoplasmic calcium in the regulation of the resting potential in the pulmonary veins myocardium in rats and mice

2016 ◽  
Vol 469 (1) ◽  
pp. 152-155 ◽  
Author(s):  
V. M. Karimova ◽  
V. S. Kuzmin ◽  
N. A. Undrovinas ◽  
L. V. Rozenshtraukh
Keyword(s):  
Pulmonary Veins ◽  
Resting Potential ◽  
Cytoplasmic Calcium ◽  
Rats And Mice

scholarly journals Ionotropic GABA Receptors and Distal Retinal ON and OFF Responses

Scientifica ◽  
2014 ◽  
Vol 2014 ◽  
pp. 1-23 ◽  
Author(s):  
E. Popova
Keyword(s):  
Gaba Receptors ◽  
Time Course ◽  
Light Adaptation ◽  
Current Knowledge ◽  
Relative Sensitivity ◽  
Bipolar Cells ◽  
Visual Signals ◽  
Gamma Aminobutyric Acid ◽  
Large Populations

In the vertebrate retina, visual signals are segregated into parallel ON and OFF pathways, which provide information for light increments and decrements. The segregation is first evident at the level of the ON and OFF bipolar cells in distal retina. The activity of large populations of ON and OFF bipolar cells is reflected in the b- and d-waves of the diffuse electroretinogram (ERG). The role of gamma-aminobutyric acid (GABA), acting through ionotropic GABA receptors in shaping the ON and OFF responses in distal retina, is a matter of debate. This review summarized current knowledge about the types of the GABAergic neurons and ionotropic GABA receptors in the retina as well as the effects of GABA and specific GABAAand GABACreceptor antagonists on the activity of the ON and OFF bipolar cells in both nonmammalian and mammalian retina. Special emphasis is put on the effects on b- and d-waves of the ERG as a useful tool for assessment of the overall function of distal retinal ON and OFF channels. The role of GABAergic system in establishing the ON-OFF asymmetry concerning the time course and absolute and relative sensitivity of the ERG responses under different conditions of light adaptation in amphibian retina is also discussed.

scholarly journals Modulation of crayfish retinal function by red pigment concentrating hormone

1995 ◽  
Vol 198 (7) ◽  
pp. 1447-1454 ◽  
Author(s):  
A Garfias ◽  
L Rodríguez-Sosa ◽  
H Aréchiga
Keyword(s):  
Circadian Rhythm ◽  
Light Adaptation ◽  
Retinal Pigment ◽  
Physiological Role ◽  
Pigment Cells ◽  
Red Pigment ◽  
Retinal Activity ◽  
Retinal Photoreceptors ◽  
Dose Dependent

The role of the crustacean octapeptide red pigment concentrating hormone (RPCH) in the control of crayfish retinal activity was explored. RPCH injection into intact animals resulted, after a latency of 10­30 min, in a dose-dependent enhancement of electroretinogram (ERG) amplitude lasting 60­120 min. RPCH was able to potentiate ERG amplitude in both light-adapted and dark-adapted animals. Following light-adaptation, responsiveness to RPCH was five times higher than following dark-adaptation. In conjunction with ERG enhancement, in light-adapted animals, RPCH injection elicited a dose-dependent retraction of distal retinal pigment, but did not affect proximal retinal pigment position. The effects of RPCH were blocked by a polyclonal antibody raised against a tyrosinated form of RPCH (A-tyr-RPCH). The antibody was also capable of partially blocking the nocturnal phase of the circadian rhythm of ERG amplitude and the darkness-induced retraction of distal retinal pigment. These results suggest that RPCH acts both on the retinal photoreceptors and on the distal pigment cells, playing a physiological role as a mediator of the effects induced by darkness and by the nocturnal phase of the circadian rhythm.

Visions of vision: Studies of the horseshoe crab compound eye

1992 ◽  
Vol 50 (1) ◽  
pp. 488-489
Author(s):  
Steven C. Chamberlain
Keyword(s):  
Horseshoe Crab ◽  
Light Adaptation ◽  
Compound Eye ◽  
Visually Guided ◽  
Morphological Process ◽  
Morphological Studies ◽  
Visual Processes ◽  
Lateral Eye ◽  
The Brain

The lateral eye of the horseshoe crab, Limulus polyphemus, is an important model system for studies of visual processes such as phototransduction, lateral inhibition, and light adaptation. It has also been the system of choice for pioneering studies of the role of circadian efferent input from the brain to the eye. For example, light and efferent input interact in controlling the daily shedding of photosensitive membrane and photomechanical movements. Most recently, modeling efforts have begun to relate anatomy, physiology and visually guided behavior using parallel computing. My laboratory has pursued collaborative morphological studies of the compound eye for the past 15 years. Some of this research has been correlated structure/function studies; the rest has been studies of basic morphology and morphological process.

scholarly journals Human T-Cell Lymphotropic Virus Type 1 p12I Expression Increases Cytoplasmic Calcium To Enhance the Activation of Nuclear Factor of Activated T Cells

2002 ◽  
Vol 76 (20) ◽  
pp. 10374-10382 ◽  
Author(s):  
Wei Ding ◽  
Björn Albrecht ◽  
Robert E. Kelley ◽  
Natarajan Muthusamy ◽  
Seung-Jae Kim ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Calcium Release ◽  
Nuclear Factor ◽  
Cytoplasmic Calcium ◽  
Activated T Cells ◽  
Human T Cell ◽  
Nfat Activation

ABSTRACT Human T-cell lymphotropic virus type 1 (HTLV-1) establishes persistent infection and is associated with lymphoproliferative or neurodegenerative diseases. As a complex retrovirus, HTLV-1 contains typical structural and enzymatic genes, as well as regulatory and accessory genes encoded in the pX region. The early events necessary for HTLV-1 to establish infection in lymphocytes, its primary target cells, remain unresolved. Recent studies have demonstrated the importance of regulatory and accessory gene products in determining this virus-host interaction. Among these, pX open reading frame I, which encodes two proteins, p12I and p27I, is required for establishing persistent infection in vivo and for infection in quiescent primary lymphocytes. In addition, p12I localizes in the endoplasmic reticulum (ER) and cis-Golgi apparatus and associates with a calcium binding protein, calreticulin. We recently reported that p12I expression induces the calcium-responsive T-cell transcription factor, nuclear factor of activated T cells (NFAT), in the presence of phorbol ester activation. Based on these studies, we hypothesize that p12I may modulate calcium release from the ER. Here, we report that p12I expression increases basal cytoplasmic calcium and concurrently diminishes calcium available for release from the ER stores. Overexpression of calreticulin, a calcium buffer protein, blocked p12I-mediated NFAT activation independently of its ability to bind p12I. Chemical inhibition studies using inhibitors of inositol 1,4,5-triphosphate receptor and calcium release-activated calcium channels suggest that inositol 1,4,5-triphosphate receptor in the ER membrane and calcium release-activated calcium channels in the plasma membrane contribute to p12I-mediated NFAT activation. Collectively, our results are the first to demonstrate the role of p12I in elevating cytoplasmic calcium, an antecedent to T-cell activation, and further support the important role of this accessory protein in the early events of HTLV-1 infection.

scholarly journals The Role of Steady Phosphodiesterase Activity in the Kinetics and Sensitivity of the Light-Adapted Salamander Rod Photoresponse

2000 ◽  
Vol 116 (6) ◽  
pp. 795-824 ◽  
Author(s):  
S. Nikonov ◽  
T.D. Lamb ◽  
E.N. Pugh
Keyword(s):  
Light Adaptation ◽  
Background Intensity ◽  
Dependent Manner ◽  
Α Subunit ◽  
Effective Lifetime ◽  
Time To Peak ◽  
Steady Level ◽  
Fractional Response ◽  
Hydrolysis Of

We investigated the kinetics and sensitivity of photocurrent responses of salamander rods, both in darkness and during adaptation to steady backgrounds producing 20–3,000 photoisomerizations per second, using suction pipet recordings. The most intense backgrounds suppressed 80% of the circulating dark current and decreased the flash sensitivity ∼30-fold. To investigate the underlying transduction mechanism, we expressed the responses as a fraction of the steady level of cGMP-activated current recorded in the background. The fractional responses to flashes of any fixed intensity began rising along a common trajectory, regardless of background intensity. We interpret these invariant initial trajectories to indicate that, at these background intensities, light adaptation does not alter the gain of any of the amplifying steps of phototransduction. For subsaturating flashes of fixed intensity, the fractional responses obtained on backgrounds of different intensity were found to “peel off” from their common initial trajectory in a background-dependent manner: the more intense the background, the earlier the time of peeling off. This behavior is consistent with a background-induced reduction in the effective lifetime of at least one of the three major integrating steps in phototransduction; i.e., an acceleration of one or more of the following: (1) the inactivation of activated rhodopsin (R*); (2) the inactivation of activated phosphodiesterase (E*, representing the complex Gα–PDE of phosphodiesterase with the transducin α-subunit); or (3) the hydrolysis of cGMP, with rate constant β. Our measurements show that, over the range of background intensities we used, β increased on average to ∼20 times its dark-adapted value; and our theoretical analysis indicates that this increase in β is the primary mechanism underlying the measured shortening of time-to-peak of the dim-flash response and the decrease in sensitivity of the fractional response.

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