scholarly journals On the selectivity of the NaChBac channel: an integrated computational and experimental analysis of sodium and calcium permeation

2017 ◽  
Vol 19 (44) ◽  
pp. 29840-29854 ◽  
Author(s):  
Carlo Guardiani ◽  
Olena A. Fedorenko ◽  
Stephen K. Roberts ◽  
Igor A. Khovanov
Keyword(s):  
Experimental Analysis ◽  
Calcium Ion ◽  
Calcium Influx ◽  
Calcium Permeation

A single calcium ion strongly binds to the glutamate ring of NaChBac that leads to the tiny calcium influx current.

scholarly journals Intracellular calcium release is more efficient than calcium influx in stimulating mitochondrial NAD(P)H formation in adrenal glomerulosa cells

1997 ◽  
Vol 328 (2) ◽  
pp. 525-528 ◽  
Author(s):  
Tibor ROHÁCS ◽  
Kálmán TORY ◽  
András DOBOS ◽  
András SPÄT
Keyword(s):  
Calcium Ion ◽  
Calcium Release ◽  
Calcium Influx ◽  
Biological Significance ◽  
Ion Concentration ◽  
Free Calcium ◽  
Mitochondrial Matrix ◽  
Free Medium ◽  
Glomerulosa Cells ◽  
Calcium Ion Concentration

We compared the effect on mitochondrial NAD(P)H formation of calcium release from intracellular stores with that of calcium influx from the extracellular space. Simultaneous measurements of cytoplasmic free calcium ion concentration and mitochondrial NAD(P)H were performed on fura-PE3-loaded single rat adrenal glomerulosa cells. The effects of equipotent stimuli in terms of the evoked Ca2+ response were compared. Angiotensin II (AII; 1 nM) induced a higher amplitude NAD(P)H response than K+ (5.6-7.6 mM). Vasopressin (1 μM) also induced a greater initial NAD(P)H formation than K+, although the Ca2+ signal evoked by the two agonists had similar amplitude. To examine the effect of Ca2+ release from internal stores we applied AII in Ca2+-free medium. We compared the effect on NAD(P)H formation of Ca2+ release with Ca2+ influx induced by K+, and with capacitative Ca2+ influx induced by AII. NAD(P)H formation in response to Ca2+ release was greater than that induced by Ca2+ influx, irrespective of whether induced by K+ or AII. Our results indicate that Ca2+, presumably released in the vicinity of mitochondria, activates mitochondrial dehydrogenases more efficiently than Ca2+ entering through the plasma membrane. These data confirm the biological significance of previous observations showing that Ca2+ released from inositol 1,4,5-trisphosphate-sensitive internal stores increases mitochondrial matrix [Ca2+] to a greater extent than extracellular Ca2+.

Analysis of intra- and intercellular calcium signaling in a mouse malignant glioma cell line

1994 ◽  
Vol 81 (3) ◽  
pp. 420-426 ◽  
Author(s):  
Toshiki Yamasaki ◽  
Kou-Ichi Enomoto ◽  
Kouzo Moritake ◽  
Takashi Maeno
Keyword(s):  
Calcium Signaling ◽  
Intracellular Calcium ◽  
Cell Line ◽  
Calcium Ion ◽  
Calcium Influx ◽  
Lucifer Yellow ◽  
Cytosolic Calcium ◽  
Ion Concentration ◽  
Content Type ◽  
Junctional Communication

✓ Intra- and intercellular calcium signaling in glioma cells was examined by mechanical stimulation of a monolayer cell line of methylcholanthrene-induced mouse ependymoblastoma, 203-glioma, with a fine round-tip glass needle. A fura-2 fluorescence image of the glioma revealed a four- to eightfold increase in the cytosolic calcium ion concentration in directly stimulated signal cells. The increased calcium spread to surrounding cells at a speed of 20 µm/sec for a distance of up to 200 µm. Calcium was transmitted between adjacent cells and even in cells up to 200 µm distant from the initially stimulated cell. Microinjection of Lucifer yellow dye showed no gap junctional communication between cells. Depletion of extracellular calcium ion inhibited both cytosolic calcium elevation and propagation to neighboring cells by mechanical stimulus. An intracellular calcium blocker, TMB-8, eliminated the cytosolic calcium mobilization in a mechanically stimulated cell, but had no effect on calcium diffusion to surrounding cells. Nifedipine and verapamil, antagonists of voltage-dependent calcium channels, did not act on the mechanically induced calcium response. This suggests that some stimulating factor may trigger transmission of calcium, which may be ejected directly from single stimulated cells and mediated via a membrane receptor but not through a gap junction. The calcium signaling in a mechanically stimulated cell may be related to both an influx and a redistribution of intracellular calcium from internal stores, while calcium propagation to neighboring cells may involve calcium influx alone.

Evidence that cobalt ion inhibition of prolactin secretion occurs at an intracellular locus

1984 ◽  
Vol 247 (3) ◽  
pp. C150-C155 ◽  
Author(s):  
C. N. Thaw ◽  
E. G. Raaka ◽  
M. C. Gershengorn
Keyword(s):  
Calcium Ion ◽  
External Surface ◽  
Calcium Influx ◽  
Divalent Cations ◽  
Prolactin Secretion ◽  
Gh3 Cells ◽  
Intracellular Camp ◽  
Maximal Effect ◽  
Cobalt Ion ◽  
Ca2 Channels

Cobalt inhibition of stimulated prolactin secretion has been interpreted as demonstrating an essential role for enhanced calcium influx in the action of thyrotropin-releasing hormone (TRH) in GH3 cells. However, this interpretation is based on the assumption that cobalt ion (Co2+) binds to the external surface of cells to antagonize calcium-mediated processes only by blocking influx of extracellular calcium ion (Ca2+). In this report, we present evidence that Co2+ acts at an intracellular locus (or loci) to inhibit prolactin secretion. When GH3 cells were incubated in medium containing 1.5 mM Ca2+, Co2+ inhibited basal as well as 50 mM K+- and TRH-induced secretion; half-maximal effect occurred between 0.1 and 0.3 mM Co2+. When cells were incubated in medium containing 0.05 and 0.003 mM Ca2+, concentrations that abolish 50 mM K+-induced prolactin secretion, Co2+ still inhibited basal and TRH-stimulated prolactin secretion. Co2+ also inhibited prolactin secretion stimulated by 1-methyl-3-isobutylxanthine, dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), and vasoactive intestinal peptide, three secretagogues that act to elevate intracellular cAMP, a mechanism which appears not to involve enhanced Ca2+ influx. Last, the presence of Co2+ within the cell was shown by fluorescence quenching of intracellularly trapped Quin 2, a chelator of divalent cations. These data demonstrate that Co2+ enters GH3 cells and that Co2+ inhibition of prolactin secretion does not involve extracellular Ca2+. We suggest that Co2+ not only blocks Ca2+ channels in GH3 cells, but it inhibits prolactin secretion at an intracellular locus (loci). Hence, inhibition by Co2+ should not be interpreted as demonstrating a requirement for Ca2+ influx in stimulated secretion.

scholarly journals A first-passage approach to diffusion-influenced reversible binding and its insights into nanoscale signaling at the presynapse

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Maria Reva ◽  
David A. DiGregorio ◽  
Denis S. Grebenkov
Keyword(s):  
Analytical Solution ◽  
Calcium Ion ◽  
Calcium Influx ◽  
Reaction Diffusion ◽  
Biophysical Parameters ◽  
First Passage ◽  
Calcium Dependent ◽  
Occupancy Probability ◽  
Electrical Impulses ◽  
Synaptic Vesicle Fusion

AbstractSynaptic transmission between neurons is governed by a cascade of stochastic calcium ion reaction–diffusion events within nerve terminals leading to vesicular release of neurotransmitter. Since experimental measurements of such systems are challenging due to their nanometer and sub-millisecond scale, numerical simulations remain the principal tool for studying calcium-dependent neurotransmitter release driven by electrical impulses, despite the limitations of time-consuming calculations. In this paper, we develop an analytical solution to rapidly explore dynamical stochastic reaction–diffusion problems based on first-passage times. This is the first analytical model that accounts simultaneously for relevant statistical features of calcium ion diffusion, buffering, and its binding/unbinding reaction with a calcium sensor for synaptic vesicle fusion. In particular, unbinding kinetics are shown to have a major impact on submillisecond sensor occupancy probability and therefore cannot be neglected. Using Monte Carlo simulations we validated our analytical solution for instantaneous calcium influx and that through voltage-gated calcium channels. We present a fast and rigorous analytical tool that permits a systematic exploration of the influence of various biophysical parameters on molecular interactions within cells, and which can serve as a building block for more general cell signaling simulators.

Lead aspartate: a new en bloc stain for electron microscopy

1978 ◽  
Vol 36 (2) ◽  
pp. 34-35
Author(s):  
J.R. Walton
Keyword(s):  
Electron Microscopy ◽  
Calcium Ion ◽  
Enzyme Reaction ◽  
Lead Citrate ◽  
Reaction Products ◽  
En Bloc ◽  
Thin Sections ◽  
Lead Salts ◽  
Thin Sectioning ◽  
High Alkalinity

In electron microscopy, lead is the metal most widely used for enhancing specimen contrast. Lead citrate requires a pH of 12 to stain thin sections of epoxy-embedded material rapidly and intensively. However, this high alkalinity tends to leach out enzyme reaction products, making lead citrate unsuitable for many cytochemical studies. Substitution of the chelator aspartate for citrate allows staining to be carried out at pH 6 or 7 without apparent effect on cytochemical products. Moreover, due to the low, controlled level of free lead ions, contamination-free staining can be carried out en bloc, prior to dehydration and embedding. En bloc use of lead aspartate permits the grid-staining step to be bypassed, allowing samples to be examined immediately after thin-sectioning.Procedures. To prevent precipitation of lead salts, double- or glass-distilled H20 used in the stain and rinses should be boiled to drive off carbon dioxide and glassware should be carefully rinsed to remove any persisting traces of calcium ion.

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