Reduced cytoplasmic calcium concentration may be both necessary and sufficient for photoreceptor light adaptation

1995 ◽  
Vol 18 (03) ◽  
pp. 481
Author(s):  
H. R. Matthews ◽  
G. L. Fain
Keyword(s):  
Calcium Concentration ◽  
Light Adaptation ◽  
Cytoplasmic Calcium ◽  
Necessary And Sufficient

Photoreceptor light adaptation is mediated by cytoplasmic calcium concentration

Nature ◽  
1988 ◽  
Vol 334 (6177) ◽  
pp. 67-69 ◽  
Author(s):  
H. R. Matthews ◽  
R. L. W. Murphy ◽  
G. L. Fain ◽  
T. D. Lamb
Keyword(s):  
Calcium Concentration ◽  
Light Adaptation ◽  
Cytoplasmic Calcium

Extracellular ATP increases [Ca 2+]i in distal tubule cells. I. Evidence for a P2Y2 purinoceptor

2000 ◽  
Vol 279 (1) ◽  
pp. F92-F101 ◽  
Author(s):  
Michel Bidet ◽  
Guy De Renzis ◽  
Sonia Martial ◽  
Isabelle Rubera ◽  
Michel Tauc ◽  
...  
Keyword(s):  
Calcium Concentration ◽  
Distal Tubule ◽  
Calcium Flux ◽  
Free Calcium ◽  
Receptor Subtype ◽  
Cytoplasmic Calcium ◽  
P2y2 Receptor ◽  
Nucleotide Analogs ◽  
Flux Measurements ◽  
Free Calcium Concentration

Experiments were performed to characterize the P2 purinoceptor subtype responsible for cytoplasmic calcium mobilization in cells from the initial part of rabbit distal convoluted tubule (DCT). Free calcium concentration was measured in a DCT cell line (DC1) with the probe fura 2. Both ATP and UTP increased cytosolic Ca2+ concentration ([Ca2+]i; EC50 3 and 6 μM, respectively). The order of potency for nucleotide analogs was ATP = UTP > adenosine 5′- O-[thiotriphosphate] ≫ ADP > UDP, which is consistent with the pharmacology of the P2Y2 receptor subtype. The increased [Ca2+]iresponses to ATP and UTP were strongly inhibited by suramin. Pretreatment of cells with pertussis toxin (PTX) attenuated the action of both nucleotides. Inhibition of phospholipase C with U-73122 totally blocked the [Ca2+]i response to ATP. Thus ATP- and UTP-stimulated [Ca2+]i mobilization in DC1 cells appears to be mediated via the activation of P2Y2 purinoceptors coupled to a G protein mechanism that is partially sensitive to PTX. Calcium flux measurements showed that lanthanum- and nifedipine-sensitive calcium channels are involved in the [Ca2+]i response to ATP.

The Effect of Changed Extracellular Calcium and Sodium Concentration on the Electroretinogram of the Crayfish Retina

1980 ◽  
Vol 35 (3-4) ◽  
pp. 308-318 ◽  
Author(s):  
H. Stieve ◽  
I. Claßen-Linke
Keyword(s):  
Dark Adaptation ◽  
Time Course ◽  
Calcium Concentration ◽  
Light Adaptation ◽  
Sodium Concentration ◽  
Strong Increase ◽  
Calcium Stores ◽  
Half Time ◽  
Astacus Leptodactylus ◽  
External Calcium

Abstract The electroretinogram (ERG) of the isolated retina of the crayfish Astacus leptodactylus evoked by strong 10 ms light flashes at constant 5 min intervals was measured while the retina was continuously superfused with various salines which differed in Ca2+ -and Na+ -concentrations. The osmotic pressure of test- and reference-saline was adjusted to be identical by adding sucrose. Results: 1. Upon raising the calcium-concentration of the superfusate in the range of 20-150 mmol/l (constant Na+ -concentration: 208 mmol/l) the peak amplitude hmax and the half time of decay t2 of the ERG both decrease gradually up to about 50% in respect to the corresponding value in reference saline. 2. The recovery of the ERG due to dark adaptation following the “weakly light adapted state” is greatly diminished in high external [Ca2+]ex. 3. Lowering the external calcium-concentration (10 →1 mmol/l) causes a small increase in hmax and a strong increase of the half time of decay t2 (about 180%). Upon lowering the calcium concentration of the superfusate to about 1 nmol/l by 1 mmol/l of the calcium buffer EDTA, a slowly augmenting diminution of the ERG height hm SLX occurs. How­ever, a strong retardation of the falling phase of the ERG characterized by an increase in t2 occurs quickly. Even after 90 min stay in the low calcium saline the retina is still not inexcitable; hmax is 5 - 10% of the reference value. The diminution of hmax occurs about six-fold faster when the buffer concentration is raised to 10 mmol/l EDTA. 4. Additional lowering of the Na+ -concentration (208 →20.8 mmol/l) in a superfusate with a calcium concentration raised to 150 mmol/l causes a strong reduction of the ERG amplitude hmax to about 10%. 5. In a superfusate containing 1 nmol/l calcium such lowering of the sodium concentration (208 → 20.8 mmol/l) causes a diminution of the ERG height to about 40% and the shape of the ERG to become polyphasic; at least two maxima with different time to peak values are observed. Interpretation: 1. The similarity of effects, namely raising external calcium concentration and light adaptation on the one hand and lowering external calcium and dark adaptation on the other hand may indicate that the external calcium is acting on the adaptation mechanism of the photoreceptor cells, presumably by influencing the intracellular [Ca2+]. 2. The great tolerance of the retina against Ca2+ -deficiency in the superfusate might be effected by calcium stores in the retina which need high Ca2+ -buffer concentrations in the superfusate to become exhausted. 3. In contrast to the Limulus ventral nerve photoreceptor there does not seem to be an antagonis­ tic effect of sodium and calcium in the crayfish retina on the control of the light channels. 4. The crayfish receptor potential seems to be composed of at least two different processes. Lowering calcium-and lowering external sodium-concentration both diminish the height and change the time course of the two components to a different degree. This could be caused by in­ fluencing the state of adaptation and thereby making the two maxima separately visible.

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.

scholarly journals Regulated Secretion of YopN by the Type III Machinery of Yersinia enterocolitica

2001 ◽  
Vol 183 (18) ◽  
pp. 5293-5301 ◽  
Author(s):  
Luisa W. Cheng ◽  
Olga Kay ◽  
Olaf Schneewind
Keyword(s):  
Yersinia Enterocolitica ◽  
Type Iii Secretion ◽  
Calcium Concentration ◽  
Environmental Changes ◽  
Environmental Concentration ◽  
Type Iii ◽  
Hybrid Proteins ◽  
Low Calcium ◽  
Membrane Envelope ◽  
Necessary And Sufficient

ABSTRACT During infection, Yersinia enterocoliticaexports Yop proteins via a type III secretion pathway. Secretion is activated when the environmental concentration of calcium ions is below 100 μM (low-calcium response). Yersiniae lacking yopN (lcrE), yscB, sycN, or tyeA do not inactivate the type III pathway even when the concentration of calcium is above 100 μM (calcium-blind phenotype). Purified YscB and SycN proteins form cytoplasmic complexes that bind a region including amino acids 16 to 100 of YopN, whereas TyeA binds YopN residues 101 to 294. Translational fusion of yopN gene sequences to the 5′ end of thenpt reporter generates hybrid proteins that are transported by the type III pathway. The signal necessary and sufficient for the type III secretion of hybrid proteins is located within the first 15 codons of yopN. Expression of plasmid-borneyopN, but not ofyopN 1–294-npt, complements the calcium-blind phenotype of yopN mutants. Surprisingly,yopN mutants respond to environmental changes in calcium concentration and secrete YopN1–294-Npt in the absence but not in the presence of calcium. tyeA is required for the low-calcium regulation of YopN1–294-Npt secretion, whereassycN and yscB mutants fail to secrete YopN1–294-Npt in the presence of calcium. Experiments withyopN-npt fusions identified two other signals that regulate the secretion of YopN. yopN codons 16 to 100 prevent the entry of YopN into the type III pathway, a negative regulatory effect that is overcome by expression of yscB andsycN. The portion of YopN encoded by codons 101 to 294 prevents transport of the polypeptide across the bacterial double membrane envelope in the presence of functional tyeA. These data support a model whereby YopN transport may serve as a regulatory mechanism for the activity of the type III pathway. YscB/SycN binding facilitates the initiation of YopN into the type III pathway, whereas TyeA binding prevents transport of the polypeptide across the bacterial envelope. Changes in the environmental calcium concentration relieve the TyeA-mediated regulation, triggering YopN transport and activating the type III pathway.

scholarly journals Bursting and calcium oscillations in pancreatic β-cells: specific pacemakers for specific mechanisms

2010 ◽  
Vol 299 (4) ◽  
pp. E517-E532 ◽  
Author(s):  
L. E. Fridlyand ◽  
N. Tamarina ◽  
L. H. Philipson
Keyword(s):  
Mathematical Models ◽  
Calcium Concentration ◽  
Calcium Oscillations ◽  
Cell Physiology ◽  
Cytoplasmic Calcium ◽  
Β Cells ◽  
Β Cell ◽  
Endoplasmic Reticulum Calcium ◽  
Key Aspects ◽  
Potential Interactions

Oscillatory phenomenon in electrical activity and cytoplasmic calcium concentration in response to glucose are intimately connected to multiple key aspects of pancreatic β-cell physiology. However, there is no single model for oscillatory mechanisms in these cells. We set out to identify possible pacemaker candidates for burst activity and cytoplasmic Ca2+ oscillations in these cells by analyzing published hypotheses, their corresponding mathematical models, and relevant experimental data. We found that although no single pacemaker can account for the variety of oscillatory phenomena in β-cells, at least several separate mechanisms can underlie specific kinds of oscillations. According to our analysis, slowly activating Ca2+-sensitive K+ channels can be responsible for very fast Ca2+ oscillations; changes in the ATP/ADP ratio and in the endoplasmic reticulum calcium concentration can be pacemakers for both fast bursts and cytoplasmic calcium oscillations, and cyclical cytoplasmic Na+ changes may underlie patterning of slow calcium oscillations. However, these mechanisms still lack direct confirmation, and their potential interactions raises new issues. Further studies supported by improved mathematical models are necessary to understand oscillatory phenomena in β-cell physiology.

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