EFFECT OF THE EXTERNAL CONCENTRATION OF CALCIUM ON THE POSTMOULT UPTAKE OF CALCIUM IN BLUE CRABS (CALLINECTES SAPIDUS)

1994 ◽  
Vol 188 (1) ◽  
pp. 1-9
Author(s):  
D Neufeld ◽  
J Cameron
Keyword(s):  
Calcium Concentration ◽  
Calcium Uptake ◽  
Callinectes Sapidus ◽  
Free Calcium ◽  
Blue Crabs ◽  
Electrochemical Gradient ◽  
External Concentration ◽  
High Calcium ◽  
Reduced Rate ◽  
Active Transport System

The rate of calcium uptake in blue crabs (Callinectes sapidus Rathbun) acclimated to 2 sea water with a calcium concentration of 1.4 mmol l-1 was dependent on the magnitude and direction of the electrochemical gradient for calcium. When transferred to water with a high calcium concentration (6 mmol l-1), the electrochemical gradient for calcium favoured diffusive influx, and calcium uptake and apparent H+ excretion increased by approximately 50 %. When transferred to water with a low calcium concentration (0.10 mmol l-1), where the electrochemical gradient for calcium strongly favoured diffusive efflux, calcium uptake ceased but apparent H+ excretion continued at a reduced rate. Crabs regulated the free calcium concentration in their blood at approximately 8 mmol l-1 when the external concentration of calcium was 1.4 mmol l-1 or higher, but the concentration of free calcium in the blood decreased to 5.6 and 4.6 mmol l-1, respectively, at external concentrations of calcium of 0.25 and 0.10 mmol l-1. Crabs transferred to water with 0.10 mmol l-1 calcium for the first 2 days after moult accumulated only 2.5 g calcium kg-1 wet mass, about one-quarter of the mass normally accumulated. Seawater-acclimated crabs transferred to 2 salinity at 1 day postmoult took up calcium at a reduced rate, indicating that a period of acclimation is necessary for a component of the active transport system to increase its capacity, for diffusive efflux to be reduced, or for both to occur.

Drosophila quail, a villin-related protein, bundles actin filaments in apoptotic nurse cells

Development ◽  
1999 ◽  
Vol 126 (24) ◽  
pp. 5645-5657 ◽  
Author(s):  
N. Matova ◽  
S. Mahajan-Miklos ◽  
M.S. Mooseker ◽  
L. Cooley
Keyword(s):  
Actin Filaments ◽  
Nurse Cell ◽  
Calcium Concentration ◽  
Developmental Model ◽  
Free Calcium ◽  
Nurse Cells ◽  
Filamentous Actin ◽  
Actin Bundle ◽  
High Calcium ◽  
Egg Chambers

Drosophila Quail protein is required for the completion of fast cytoplasm transport from nurse cells to the oocyte, an event critical for the production of viable oocytes. The abundant network of cytoplasmic filamentous actin, established at the onset of fast transport, is absent in quail mutant egg chambers. Previously, we showed that Quail is a germline-specific protein with sequence homology to villin, a vertebrate actin-regulating protein. In this study, we combined biochemical experiments with observations in egg chambers to define more precisely the function of this protein in the regulation of actin-bundle assembly in nurse cells. We report that recombinant Quail can bind and bundle filamentous actin in vitro in a manner similar to villin at a physiological calcium concentration. In contrast to villin, Quail is unable to sever or cap filamentous actin, or to promote nucleation of new actin filaments at a high calcium concentration. Instead, Quail bundles the filaments regardless of the calcium concentration. In vivo, the assembly of nurse-cell actin bundles is accompanied by extensive perforation of the nurse-cell nuclear envelopes, and both of these phenomena are manifestations of nurse-cell apoptosis. To investigate whether free calcium levels are affected during apoptosis, we loaded egg chambers with the calcium indicator Indo-1. Our observations indicate a rise in free calcium in the nurse-cell cytoplasm coincident with the permeabilization of the nuclear envelopes. We also show that human villin expressed in the Drosophila germline could sense elevated cytoplasmic calcium; in nurse cells with reduced levels of Quail protein, villin interfered with actin-bundle stability. We conclude that Quail efficiently assembles actin filaments into bundles in nurse cells and maintains their stability under fluctuating free calcium levels. We also propose a developmental model for the fast phase of cytoplasm transport incorporating findings presented in this study.

scholarly journals Calcium metabolism and cardiovascular function after spaceflight

2002 ◽  
Vol 92 (1) ◽  
pp. 3-12 ◽  
Author(s):  
Daniel C. Hatton ◽  
Qi Yue ◽  
Jacqueline Dierickx ◽  
Chantal Roullet ◽  
Keiichi Otsuka ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Calcium Metabolism ◽  
Calcium Concentration ◽  
Dietary Calcium ◽  
Ionized Calcium ◽  
Free Calcium ◽  
Mineral Density ◽  
Spontaneously Hypertensive ◽  
Low Calcium ◽  
High Calcium

To determine the influence of dietary calcium on spaceflight-induced alterations in calcium metabolism and blood pressure (BP), 9-wk-old spontaneously hypertensive rats, fed either high- (2%) or low-calcium (0.02%) diets, were flown on an 18-day shuttle flight. On landing, flight animals had increased ionized calcium ( P < 0.001), elevated parathyroid hormone levels ( P < 0.001), reduced calcitonin levels ( P < 0.05), unchanged 1,25(OH)2D3levels, and elevated skull ( P < 0.01) and reduced femur bone mineral density. Basal and thrombin-stimulated platelet free calcium (intracellular calcium concentration) were also reduced ( P < 0.05). There was a tendency for indirect systolic BP to be reduced in conscious flight animals ( P = 0.057). However, mean arterial pressure was elevated ( P < 0.001) after anesthesia. Dietary calcium altered all aspects of calcium metabolism ( P < 0.001), as well as BP ( P < 0.001), but the only interaction with flight was a relatively greater increase in ionized calcium in flight animals fed low- compared with high-calcium diets ( P < 0.05). The results indicate that 1) flight-induced disruptions of calcium metabolism are relatively impervious to dietary calcium in the short term, 2) increased ionized calcium did not normalize low-calcium-induced elevations of BP, and 3) parathyroid hormone was paradoxically increased in the high-calcium-fed flight animals after landing.

Postmoult Uptake of Calcium by the Blue Crab (Callinectes Sapidus) in Water of low Salinity

1992 ◽  
Vol 171 (1) ◽  
pp. 283-299 ◽  
Author(s):  
DOUGLAS S. NEUFELD ◽  
JAMES N. CAMERON
Keyword(s):  
Calcium Uptake ◽  
Sea Water ◽  
Callinectes Sapidus ◽  
Whole Body ◽  
Equilibrium Potential ◽  
Free Calcium ◽  
Moult Cycle ◽  
Transepithelial Potential ◽  
Low Salinity ◽  
Calcium Magnesium

After moulting, blue crabs (Callinectes sapidus) acclimated to a salinity of 2‰ were able to calcify as rapidly and accumulate as much calcium as crabs in sea water. Immediately after moult, the total masses of calcium, magnesium and strontium present in the whole body were 4.6, 15.6 and 3.0%, respectively, of their intermoult values. During the time of most rapid calcification, calcium uptake was 5.4±1.4mmoll−1, which is comparable to the maximum rate found in seawater-acclimated crabs. The concentrations of bound and free calcium in the blood changed very little with acclimation salinity, remaining at approximately 3 and 8mmoll−1, respectively, both during intermoult and 1 day postmoult. Free calcium changed relatively little through the moult cycle, varying between 6.9 and 8.1mmoll−1, but bound calcium rose to a peak of 6.4mmoll−1 prior to moult then dropped to 2.6mmoll−1 after moult, concurrent with a decrease of approximately 80% in the protein concentration of the blood. The concentration of total magnesium in the blood increased from a premoult low of 9.0mmoll−1 to a postmoult high of 11.7mmoll−1 and remained elevated throughout the period of rapid mineralization. During the postmoult period of rapid calcium uptake, the internal-to-external concentration ratio for total calcium was 6.6 to 1. The activity ratio, however, was only 2.5 to 1 because 28% of the calcium in the blood was bound to protein, and because the lower ionic strength of the medium resulted in a 2.5-fold higher activity coefficient for the water compared to blood. The transepithelial potential at postmoult (−5.4±0.7mV) was significantly more negative than at intermoult (−3.1±0.6mV). In artificial 2‰ sea water, the transepithelial potential (−9.3±0.7mV) was higher than the equilibrium potential for calcium (−12.0±0.5mV), implicating active transport in the uptake of calcium.

Calcium Regulation in the Freshwater Crayfish Austropotamobius Pallipes (Lereboullet)

1972 ◽  
Vol 57 (2) ◽  
pp. 471-487
Author(s):  
PETET GREENAWAY
Keyword(s):  
Active Transport ◽  
Calcium Concentration ◽  
Calcium Uptake ◽  
Calcium Regulation ◽  
Freshwater Crayfish ◽  
Calcium Balance ◽  
Electrochemical Gradient ◽  
Austropotamobius Pallipes ◽  
Calcium Loss ◽  
Normal Calcium

1. Calcium regulation in normal and in calcium-depleted specimens of Austropotamobius pallipes in the intermoult condition has been investigated. 2. Calcium turnover was very low and the normal calcium balance was negative for much of the winter intermoult stage. 3. Calcium uptake was against a small electrochemical gradient, at least part of the influx occurring by active transport. 4. Most of the calcium loss occurred across the gills, and the urine contribution was small. 5. Calcium-depleted animals showed only a small fall in haemolymph calcium concentration and calcium uptake was not significantly increased by depletion.

Hypothalamic Hypophyseal Inhibitory Factor (HHIF) Increases Intrasynaptosomal Free Calcium Concentration

Hypertension ◽  
1997 ◽  
Vol 29 (6) ◽  
pp. 1337-1343 ◽  
Author(s):  
Mercedes Ricote ◽  
Elena Garcia-Martin ◽  
Jose Sancho ◽  
Carlos Gutierrez-Merino
Keyword(s):  
Calcium Concentration ◽  
Inhibitory Factor ◽  
Free Calcium ◽  
Free Calcium Concentration

Identification of ecto-PKC on surface of human platelets: role in maintenance of latent fibrinogen receptors

2000 ◽  
Vol 278 (6) ◽  
pp. H2008-H2019 ◽  
Author(s):  
Anna Babinska ◽  
Michael V. Hogan ◽  
Tomasz Sobocki ◽  
Malgorzata B. Sobocka ◽  
Yigal H. Ehrlich ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Calcium Concentration ◽  
Surface Protein ◽  
Human Platelets ◽  
Surface Proteins ◽  
Free Calcium ◽  
Platelet Surface ◽  
Inhibitory Peptides ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration

Human platelets express a protein phosphorylation system on their surface. A specific protein kinase C (PKC) antibody, monoclonal antibody (MAb) 1.9, which binds to the catalytic domain of PKC and inhibits its activity, causes the aggregation of intact platelets while inhibiting the phosphorylation of platelet surface proteins. Photoaffinity labeling with 100 nM 8-azido-[α32P]ATP identified this ecto-PKC as a single surface protein of 43 kDa sensitive to proteolysis by extracellular 0.0005% trypsin. Inhibition of the binding of 8-azido-[α32P]ATP to the 43-kDa surface protein by MAb 1.9 identified this site as the active domain of ecto-PKC. Covalent binding of the azido-ATP molecule to the 43-kDa surface protein inhibited the phosphorylative activity of the platelet ecto-PKC. Furthermore, PKC pseudosubstrate inhibitory peptides directly induced the aggregation of platelets and inhibited azido-ATP binding to the 43-kDa protein. Platelet aggregation induced by MAb 1.9 and by PKC inhibitory peptides required the presence of fibrinogen and resulted in an increase in the level of intracellular free calcium concentration. This increase in intracellular free calcium concentration induced by MAb 1.9 was found to be dependent on the binding of fibrinogen to activated GPIIb/IIIa integrins, suggesting that MAb 1.9 causes Ca2+flux through the fibrinogen receptor complex. We conclude that a decrease in the state of phosphorylation of platelet surface proteins caused by inhibition of ecto-PKC results in membrane rearrangements that can induce the activation of latent fibrinogen receptors, leading to platelet aggregation. Accordingly, the maintenance of a physiological steady state of phosphorylation of proteins on the platelet surface by ecto-PKC activity appears to be one of the homeostatic mechanisms that maintain fibrinogen receptors of circulating platelets in a latent state that cannot bind fibrinogen.

The origin of passive force enhancement in skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. C74-C78 ◽  
Author(s):  
V. Joumaa ◽  
D. E. Rassier ◽  
T. R. Leonard ◽  
W. Herzog
Keyword(s):  
Calcium Concentration ◽  
Force Production ◽  
Primary Source ◽  
Passive Force ◽  
Active Force ◽  
Force Enhancement ◽  
Bridge Formation ◽  
Calcium Dependent ◽  
Cross Bridge ◽  
High Calcium

The aim of the present study was to test whether titin is a calcium-dependent spring and whether it is the source of the passive force enhancement observed in muscle and single fiber preparations. We measured passive force enhancement in troponin C (TnC)-depleted myofibrils in which active force production was completely eliminated. The TnC-depleted construct allowed for the investigation of the effect of calcium concentration on passive force, without the confounding effects of actin-myosin cross-bridge formation and active force production. Passive forces in TnC-depleted myofibrils ( n = 6) were 35.0 ± 2.9 nN/ μm2 when stretched to an average sarcomere length of 3.4 μm in a solution with low calcium concentration (pCa 8.0). Passive forces in the same myofibrils increased by 25% to 30% when stretches were performed in a solution with high calcium concentration (pCa 3.5). Since it is well accepted that titin is the primary source for passive force in rabbit psoas myofibrils and since the increase in passive force in TnC-depleted myofibrils was abolished after trypsin treatment, our results suggest that increasing calcium concentration is associated with increased titin stiffness. However, this calcium-induced titin stiffness accounted for only ∼25% of the passive force enhancement observed in intact myofibrils. Therefore, ∼75% of the normally occurring passive force enhancement remains unexplained. The findings of the present study suggest that passive force enhancement is partly caused by a calcium-induced increase in titin stiffness but also requires cross-bridge formation and/or active force production for full manifestation.

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