Synaptic transmission at high pressure: Effects of [Ca2+]o

• 1.1. The effects of pressure on synaptic currents were examined in crayfish abdominal muscles.
• 2.2. Helium pressure (10.1 MPa) considerably decreased extracellulariy-recorded excitatory junctional potentials associated with increased short-term facilitation.
• 3.3. These effects could be mimicked by a reduction of [Ca²⁺]_o, and partially compensated by an increase in [Ca²⁺]_o.
• 4.4. Pressure also reduced the amplitude of the extracellular nerve terminal potentials (ENTP) by up to 25%, and significantly increased synaptic delay in a [Ca²⁺]_o-dependent manner.
• 5.5. The interaction between compression and various [Ca²⁺]_o were analysed in terms of an existing model of transmitter release. The results were consistent with the hypothesis that high pressure decreases the maximal Ca²⁺ influx into nerve terminals.
• 6.6. The decreased ENTP and increased synaptic delay suggest that additional processes may be involved in pressure effects on synaptic transmission.

     

Crayfish retinular cells: Influence of extracellular sodium and calcium upon receptor potential

• 1.1. In crayfish, light stimulation of the retinular cells induces a depolarizing receptor potential.
• 2.2. Experiments were designed to determine the role of Na⁺ and Ca²⁺ on receptor potential during dark And light states.
• 3.3. Depolarization depends on Na⁺ and Ca²⁺ availability to the retinular cell.
• 4.4. Repolarization velocity and response duration depend on extracellular Ca²⁺ availability.
• 5.5. Light adaptation increases receptor potential dependence on calcium and sodium ions.
• 6.6. We analyse these results with respect to other invertebrate photoreceptors.

     

Uptake and release of calcium ions by heavy sarcoplasmic reticulum fraction of normal and malignant hyperthermia-susceptible human skeletal muscle

• 1.1. Ca²⁺ uptake, Ca²⁺-dependent ATPase activity and halothane-induced Ca²⁺ release from the heavy sarcoplasmic reticulum fraction of muscle from malignant hyperthermia susceptible individuals are similar to those of normal human muscle.
• 2.2. Ca²⁺-induced Ca²⁺ release from the diseased muscle was increased by 13%.

     

The possibility that Ca2+-ATPase from the plasma membrane-rich fraction of bovine parotid gland is ecto-Ca2+-dependent nucleoside triphosphatase

• 1.1. Parotid plasma membrane nonpump low-affinity Ca²⁺-ATPase, which possesses high-affinity (Ca²⁺ + Mg²⁺ )-ATPase activity, was characterized.
• 2.2. Purified Ca²⁺-ATPase hydrolyzed the nucleoside triphosphates, GTP, ITP, CTP, UTP, TTP (67–93% of ATP) and nucleoside diphosphates, ADP. GDP, IDP, CDP, TDP (12–40% of ATP) but not AMP and p-NPP.
• 3.3. The maximum activities of Ca²⁺- and (Ca²⁺ +Mg²⁺ )-ATPases were obtained in the presence of 1 mM and 0.13 μ M Ca²⁺, respectively.
• 4.4. The K_m values for Ca²⁺ in Ca²⁺- and (Ca²⁺+ Mg²⁺ )-ATPases were 0.2 mM and 22 nM. respectively.
• 5.5. The activities of both Ca²⁺- and (Ca²⁺ + Mg²⁺ )-ATPases were found in the right-side-out-vesicles obtained from the plasma membrane-rich fraction.
• 6.6. These features suggest that Ca²⁺-ATPase is an ecto-Ca²⁺-dependent nucleoside triphosphatase.

     

The role of phosphoinositide metabolism in Ca2+ signalling of skeletal muscle cells

• 1.1. The mobilization of Ca²⁺ from intracellular stores by d-myo-inositol 1,4,5-triphosphate[Ins(1,4,5)P₃] is now widely accepted as the primary link between plasma membrane receptors that stimulate phospholipase C and the subsequent increase in intracellular free Ca²⁺ that occurs when such receptors are activated (Berridge, 1993). Since the observations of VoIpe et al. (1985) which showed that Ins(1,4,5)P₃ could induce Ca²⁺ release from isolated terminal cisternae membranes and elicit contracture of chemically skinned muscle fibres, research has focused on the role of Ins(1,4,5)P₃ in the generation of SR Ca²⁺ transients and in the mechanism of excitation-contraction coupling (EC-coupling).
• 2.2. The mechanism of signal transduction at the triadic junction during EC-coupling is unknown. Asymmetric charge movement and mechanical coupling between highly specialized triadic proteins has been proposed as the primary mechanism for voltage-activated generation of SR Ca²⁺ signals and subsequent contraction. Ins(1,4,5)P₃ has also been proposed as the major signal transduction molecule for the generation of the primary Ca²⁺ transient produced during EC-coupling.
• 3.3. Investigations on the generation of Ca²⁺ transients by Ins(1,4,5)P₃ have been conducted on ion channels incorporated into lipid bilayers, skinned and intact fibres and isolated membrane vesicles. Ins(1,4,5)P₃ induces SR Ca²⁺ release and the enzymes responsible for its synthesis and degradation are present in muscle tissue. However, the sensitivity of the Ca²⁺ release mechanism to Ins(l,4,5)P₃ is highly dependent on experimental conditions and on membrane potential.
• 4.4. While Ins(1,4,5)P₃ may not be the major signal transduction molecule for the generation of the primary Ca²⁺ signal produced during voltage-activated contraction, this inositol polyphosphate may play a functional role as a modulator of EC-coupling and/or of the processes of myoplasmic Ca²⁺ regulation occurring on a time scale of seconds, during the events of contraction.

     

Bioelectrical potentials across the mantle epithelium of Achatina fulica

• 1.1. The shell side of the mantle of Achatina fulica is several millivolts positive to the blood side in vitro.
• 2.2. The electrical potential does not depend on Na⁺, Ca²⁺, Mg²⁺, K⁺ or HCO₃⁻ but requires the presence of chloride on the shell side.
• 3.3. The potential difference and short-circuit current ranged from 3.0 to 30.0 mV and 15.0 to 75 μA/cm² with averages at 10m V and 50 μA/cm² respectively.
• 4.4. The electrical gradient is reduced by 2,4-dinitrophenol, thiocyanate and furosemide but not by ouabain, CO₂ or acetozolamide.
• 5.5. It is suggested that the nature and mechanism of electrogenesis in Achatina parallels that of the Helix mantle.

     

PLA2 activity in rat liver nuclei

• 1.1. Subcellular fractions of rat liver were assayed for PLA₂ activity.
• 2.2. The PLA₂ assay measures the release of [³ H]oleic acid from phospholipids, using labeled E. coli as substrate.
• 3.3. Nuclear fractions contained PLA₂ activity, which was Ca²⁺ dependent and could not be explained from mitochondrial, microsomal or plasma membrane contamination.
• 4.4. The V_max value of nuclear PLA₂ is 0.30 ± 0.04 pmol oleic acid/min/mg protein; its K_m value is 0.86±0.12μM, similar to that of mitochondrial PLA₂.
• 5.5. We conclude that rat liver nuclei contain PLA₂ activity.

     

Modulation of the ATP induced [Ca2+]c increase in as-30D hepatoma cells

• 1.1. The regulation of the increase in the cytosolic calcium concentration ([Ca²⁺]c) induced by extracellular ATP in AS-30D hepatoma cells was studied.
• 2.2. Homologous desensitization involving the refilling of intracellular calcium pools and the participation of protein kinase C was found.
• 3.3. Isoproterenol, forskolin and dibutyril-cyclic AMP also induced an increase in [Ca²⁺]c.
• 4.4. Interestingly, synergism was found for isoproterenol or forskolin and ATP.
• 5.5. The results suggest that there are two pathways for mobilizing [Ca²⁺] in AS-30D hepatoma cells; one is activated by ATP receptors and the other by cyclic AMP.

     

Evidence that both Ca2+-ATPase and (Ca2+ + Mg2+)-ATPase activities in the plasma membrane-rich fraction from bovine parotid gland reside on the same enzyme molecule

• 1.1. Evidence was obtained that activities of both low-affinity Ca²⁺-ATPase and high-affinity (Ca²⁺ + Mg²⁺)-ATPase in the plasma membrane-rich fraction from bovine parotid gland reside on the same enzyme.
• 2.2. Two solubilized ATPases were purified by four steps of HPLC; and both activities eluted at the same fractions from each column, and the specific activity ratio of the two enzymes at each step was constant.
• 3.3. By non-denaturing PAGE, the final preparation gave a single band for both protein staining and activity staining for the two ATPases; and the Ca²⁺-ATPase activity comigrated with that of (Ca²⁺ + Mg²⁺)-ATPase.
• 4.4. In SDS-PAGE, each activity staining for the ATPases also gave a single band, and both activities comigrated.
• 5.5. These findings suggest that Ca²⁺-ATPase and (Ca²⁺ + Mg²⁺)-ATPase are a single enzyme.

     

Phosphofructokinase from the anterior byssus retractor muscle of Mytilvs edulis: Modification of the enzyme in anoxia and by endogenous protein kinases

• 1.1. Anoxia exposure resulted in a stable modification of the kinetic properties of 6-phosphofructo-1-kinase (PFK) from the anterior byssus retractor muscle (ABRM) of the sea mussel Mytilus edulis L.
• 2.2. Compared to the aerobic enzyme, the anoxic form of PFK. showed a reduced affinity for both substrates, fructose-6-phosphate (F6P) and ATP, and an increased sensitivity to inhibition by phosphoenolpyruvate.
• 3.3. To analyze the involvement of protein kinases in the modification of PFK, extracts from aerobic or anoxic muscle were incubated with ATP and Mg²⁺ plus protein kinase second messengers cyclic 3',5'-adenosine monophosphate (cAMP), cyclic 3',5'-guanosine monophosphate (cGMP) or Ca²⁺ plus phorbol 12-myristate 13-acetate (PMA).
• 4.4. Both forms of the enzyme responded to the presence of cAMP with a strong increase in affinity for F6P.
• 5.5. In response to cGMP affinity of the aerobic enzyme for F6P decreased whereas that of the anoxic enzyme form was not affected (at 0.5 mM ATP) or increased (at 3 mM ATP).
• 6.6. Incubation with Ca²⁺ + PMA had only a limited effect on PFK kinetics but appeared to enhance the response to cGMP when the three compounds were given together.
• 7.7. Treatment of PFK-aerobic with alkaline phosphatase resulted in a strong decrease in enzyme activity and affinity for F6P; subsequent treatment with cAMP reversed the effect on S_0.5 F6P.
• 8.8. The data indicate that PFK activity is altered during the aerobic-anaerobic transition by a change in the phosphorylation state of the enzyme and that cAMP and cGMP act oppositely to regulate PFK activity, and thereby alter glycolytic rate, during this transition.

     

Renal response to hypoxia in carp,Cyprinus carpio: Changes in glomerular filtration rate,urine and blood properties and plasma catecholamines of carp exposed to hypoxic conditions

• 1.1. Changes in glomerular nitration rate (GFR), urine and blood properties and plasma catecholamines of carp were investigated during and following hypoxia.
• 2.2. GFR and urine flow decreased with increased urinary concentrations of bio-components, except protein, in the course of hypoxia.
• 3.3. Decreases in blood pH, and increases in haematocrit value and plasma K⁺, Ca²⁺, Mg²⁺, inorganic phosphate (P_i), ammonia, lactic acid and catecholamines (CAs) were observed as hypoxia progressed.
• 4.4. Increased GFR and urine flow, and higher values for urinary components, except protein, compared with those of the control were found in the initial post-stress stage.
• 5.5. The possible significance of increased plasma CAs in relation to changes in renal function in hypoxic carp is discussed.

     

Ca2+-binding and protein-protein interaction domains of the sea urchin extraembryonic coat protein hyalin

• 1.1. As reported previously (Hopper and Robinson, 1990; Int. J. Biochem. 22, 1165–1170) the sea urchin extraembryonic coat protein hyalin undergoes a Ca²⁺-induced self-association into an insoluble gel (gelation) in the presence of Mg²⁺ and/or NaCl.
• 2.2. A 275 kDa peptide fragment, generated by limited tryptic digestion of hyalin, binds Ca²⁺+ but does not undergo gelation in the presence of Ca²⁺, Mg²⁺ and NaCl.
• 3.3. Comparisons between the capacities of hyalin and the 275 kDa peptide fragment to bind Ca²⁺ indicate that the latter binds 88% less Ca²⁺ than hyalin.
• 4.4. However, the presence of Ca²⁺ alone, at a concentration of 5 mM, protects the 275 kDa peptide fragment from further digestion by trypsin mimicking the effect of this cation in protecting hyalin.
• 5.5. Gel exclusion Chromatographie analyses of the 275 kDa peptide fragment, both in the presence and absence of 5 mM Ca²⁺, indicate that this cation does induce self-association of the fragment.
• 6.6. These results provide information on the organization of the functional domains on hyalin which are required for gel formation.

     

High-affinity Ca2+-Mg2+-ATPase in kidney of euryhaline Gillichthys mirabilis: kinetics,subcellular distribution and effects of salinity

• 1.1. Two components of Ca²⁺-Mg²⁺-ATPase are observed in kidneys of G. mirabilis. The high-affinity component has a K_0.5Ca of 0.23μM; the low-affinity activity K_0.5Ca is 90–110μM. The high-affinity activity requires Mg²⁺, displays Michaelis-Menten kinetics, has peak activity at 1.2 μM Ca²⁺, and is insensitive to ouabain and Na⁺ azide.
• 2.2. In subcellular fractions, the high-affinity component segregates with Na⁺-K⁺-ATPase and is localized predominantly in BLM. The low-affinity component is broadly distributed among membranous organelles, including brush border, and may be equivalent to alkaline phosphatase.
• 3.3. Specific activity of the high-affinity Ca²⁺-Mg²⁺-ATPase is modestly increased following adaptation of fish to FW, but total renal high-affinity activity is greatest in the hypertrophied kidneys of FW-adapted fish and is least in kidneys of fish adapted to 200% SW.
• 4.4. High-affinity Ca²⁺-Mg²⁺-ATPase may be associated with active Ca²⁺ transport or with regulation of intracellular Ca²⁺ concentration of tubular cells.

     

microRNA-222 Attenuates Mitochondrial Dysfunction During Transmissible Gastroenteritis Virus Infection

1. Download : Download high-res image (93KB)
2. Download : Download full-size image

Highlights

• •microRNA-222 attenuates TGEV-induced mitochondrial dysfunction.
• •microRNA-222 downregulates THBS1 and CD47.
• •THBS1 is the target of microRNA-222 during TGEV infection.
• •THBS1 and CD47 increase mitochondrial Ca²⁺ level and reduced mitochondrial membrane potential (MMP).

     

Internal reference standards in ionic regulation and the predictability of ionic concentrations in animals

• 1.1. The regulation of ions at similar concentrations in most individuals of a species suggests the existence of internal reference standards.
• 2.2. Few have been identified, but many probably relate to cell membrane properties, including potentials, surface charge densities and equilibrium constants of receptor molecules.
• 3.3. Solubility may sometimes determine the product [Ca²⁺][CO₃²⁻].
• 4.4. Reference standards must generally each relate to more than one ionic species.
• 5.5. For some concentrations, including osmolality, there may be no direct reference standard.

     

The digestive enzymes of the pacific brown shrimp Penaeus californiensis.: I—Properties of amylase activity in the digestive tract

• 1.1. Crude extract of the whole digestive tract from the brown shrimp (P. californiensis) was investigated for digestive amylase activity.
• 2.2. Considerable amylase activity was found at pH 6.5–8.0, with optimum pH at around 7.5.
• 3.3. Optimum temperature was found between 30–40°C, similar to amylases from other crustaceans.
• 4.4. Amylase activity was highly halotolerant, having 50% maximum activity at 3 M NaCl.
• 5.5. Maximum amylase activity was found at 0.01 M NaCl.
• 6.6. Amylase activity was partially inhibited by the divalent ions Hg²⁺, Zn²⁺, Cu²⁺ and Cr²⁺.
• 7.7. Mg²⁺ and Ca²⁺ ions seemed to enhance amylase activity.

     

Possible role of ca2+ in heavy metal cytotoxicity

• 1.1. Organic xenobiotic metabolism often results in oxidative stress, involving GSH depletion, alteration of thiol/disulphide balance and peroxidation of membrane lipids. These events can lead to the disruption of Ca²⁺ homeostasis, through impairment of the Ca²⁺ translocases present in cellular membranes. Inhibition of the activity of Ca,Mg-ATPases due to oxidation of their SH groups would lead to uncontrolled rises in cytosolic Ca²⁺ levels resulting in loss of cell viability.
• 2.2. These observations seem to be of interest when interpreting the biochemical mechanisms of heavy metal cytotoxicity. Since these cations (such as Hg²⁺, Cu²⁺, Cd²⁺ and Zn) have an extremely high affinity for SH groups, they may affect the function of SH containing proteins, such as the Ca,Mg-ATPases, as in the case of oxidative stress.
• 3.3. Results are reported indicating that Hg²⁺ may stimulate Ca²⁺ influx through voltage-dependent channels in different experimental systems. Moreover, evidence is presented that heavy metals can inhibit Ca,Mg-ATPase activity and affect mitochondrial functions in the cells of different organisms.
• 4.4. The possibility that heavy metal cytotoxicity is mediated through disruption of Ca²⁺ homeostasis is discussed.

     

Behaviour and haemolymphatic ionic composition of the intertidal crab Chasmagnathus granulata dana, 1851 (Crustacea: Decapoda) during emersion

• 1.1. Behavioural observations and haemolymphatic measurements of Na⁺ K⁺ and Ca⁺ were performed in Chasmagnalhus granulata during emersion.
• 2.2. Activity levels were found to be higher during voluntary emersion periods than when the animals were submerged. A lt₅₀ of 39.45 hr was observed when no access to water was allowed.
• 3.3. The Na⁺ and K⁺ and Ca⁺ levels increased during aerial exposure. The Na⁺ and K⁺ levels were restored prior the end of the experimental period. Mechanisms for such regulation are therefore discussed. The Ca²⁺ levels, remaining high during emersion, are probably a result of acid-base balance adjustments.

     

The sea urchin extraembryonic hyaline layer: Ionic parameters controlling the hyalin gelation reaction

• 1.1. As reported previously (Robinson, 1988) the Ca²⁺-induced self-association reaction of the protein hyalin, purified from the sea urchin extraembryonic hyaline layer, was modulated by both Mg²⁺ and NaCl.
• 2.2. In the presence of 400 mM NaCl the apparent dissociation constant (Ca²⁺) decreased five-fold from 4.8 ± 1.1 mM in the absence to 0.9 ± 0.5 mM in the presence of 20 mM Mg²⁺.
• 3.3. The potentiating effect of Mg²⁺ occurred with an apparent dissociation constant (Mg²⁺) of 4.6 ± 0.5mM.
• 4.4. In the absence of Ca²⁺ or NaCl hyalin dissociated from isolated hyaline layers indicating that the behavior of hyalin within the layer is predictable from results obtained with the purified protein.

     

Biochemical characterization of the plasma membrane Ca2+ pumping ATPase activity present in the gill cells of Mytilus galloprovincialis LAM

• 1.1. In the plasma membrane of mussel gill cells an ouabain insensitive, Ca²⁺-activated ATPase activity is present. The ATPase has high Ca²⁺ affinity (K_ma = 0.3 μM).
• 2.2. The optimum assay conditions to evaluate the enzymatic activity of the Ca²⁺-stimulated ATPase at 19°C are: 120–300 mM KCl ionic strength, pH 7.0 and 2 mM ATP. As for mammalian enzymes, the Ca²⁺ ATPase activity is stimulated by DTT (0.5–1 mM) and it is inhibited by low concentrations of vanadate (10–50 μM) and -SH inhibitors such as PCMB and PCMBS (10 μM); the enzyme appears to be calmodulin insensitive.
• 3.3. Electrophoretic analyses of plasma membrane proteins demonstrate that: (a) Ca²⁺ at n-μM concentrations is necessary to activate ATP hydrolysis with consequent formation of the enzyme-phosphate complex; (b) the steady state concentration of the phosphorylated intermediate is increased in the presence of La³⁺; (c) the mol. wt of Ca²⁺ ATPase is about 140 kDa.
• 4.4. Low Ca²⁺ concentrations (n-μM) are sufficient to stimulate the ATP-dependent Ca²⁺ uptake by plasma membrane inside-out vesicles.
• 5.5. The results indicate that the Ca²⁺ pump present in the gill plasma membranes could be responsible for Ca²⁺ extrusion and therefore involved in maintaining the cytosolic Ca²⁺ concentration within physiological levels.