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1.
  • 1.1. Release of creatine kinase (CK) in the Ca2+ paradox of the Langendorff-perfused rat heart is dependent on the conditions of Ca2+ depletion and Ca2+ repletion.
  • 2.2. CK release is reduced by raising [Ca2+]o during Ca2+ depletion and progressively increased by extending the Ca2+ free period from 2 to 5 min.
  • 3.3. CK release is reduced by decreasing the electrochemical gradient for Ca2+ during Ca2+ repletion.
  • 4.4. The findings are discussed in the light of current hypotheses for the biochemical mechanisms that underlie the Ca2+ paradox.
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2.
  • 1.1. Heparin stimulates the activity of nonactivated and activated skeletal muscle phosphorylase kinase in a Ca2+-dependent manner.
  • 2.2. The stimulatory effect of heparin on the activity of nonactivated phosphorylase kinase is also expressed in the presence of calmodulin and glycogen. Heparin acted in synergism with glycogen.
  • 3.3. Heparin increases the affinity of phosphorylase kinase to Ca2+ 5–12 fold depending upon the activation conditions.
  • 4.4. Ca2+ influences the stimulation of liver phosphorylase kinase by heparin in a similar way.
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3.
  • 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.
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4.
  • 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.
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5.
  • 1.1. Single skeletal muscle fibers were transferred from a normal Ringer solution to Na+ ion free solution, and vice versa, and tetanus responses were recorded immediately after the transfer.
  • 2.2. Fractional tetanus tension recorded immediately after the displacement from the Na+ ion free solution to normal Ringer solution was dependent on fiber diameter.
  • 3.3. Diffusion of Na+ ions along the transverse tubules was simulated [apparent diffusion constant was 3.11 × 10−6 (cm2/s)].
  • 4.4. Our results suggest that the electrotonic spreading of membrane potential, caused by an action potential in the transverse tubules, could release Ca2+ ions from sarcoplasmic reticulum.
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6.
  • 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.
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7.
  • 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.
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8.
  • 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 Km 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.
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9.
  • 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.
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10.
  • 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.
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11.
  • 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.
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12.
  • 1.1. Rainbow trout were acclimated to salt water (1.5, 2.0 or 3.0%, which means 40, 60 or 85% concentrated sea-water) and the electrolyte, glucose and cortisol concentrations of the plasma as well as the extra- and intracellular muscle space, the muscle electrolyte concentrations and the ATPase activity were analysed.
  • 2.2. Plasma osmolality, Na+, Ca2+ and Mg2+ concentrations of the plasma had a maximum at 24 hr after the start of acclimation when acclimated to 3.0% salt water. Plasma osmolality, Na+ and Mg2+ concentrations were significantly higher during the whole acclimation time when exposed to 3.0% salt water.
  • 3.3. Variations and regulations of ECS and ICS were clearly demonstrated. The intracellular electrolyte concentrations were also maximal at 24 hr.
  • 4.4. The plasma glucose level was just slightly elevated, but the cortisol level clearly indicated a stress response at 24 hr.
  • 5.5. The activity of gill Na-K-ATPase increased during the acclimation time.
  • 6.6. The regulatory processes in trout during acclimation to salt water are compared with those occurring in tilapia and carp.
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13.
  • 1.1. Synaptic plasma membrane vesicles (SPMV) from rat brain synthesized ceramide-phosphoethanolamine (SpE), an analogue of sphingomyelin (SpC) from phosphatidylethanolamine (PE) and ceramide.
  • 2.2. This reaction was catalyzed by PE: ceramide-phosphotransferase.
  • 3.3. The presence of PC did not modify the SpE synthesis and PI and PS at twice PE concentration seemed to be activators; only PG was an inhibitor at all concentrations.
  • 4.4. Some cations (Mg2+, Mn2+) were without effect, while Ca2+ increased transferase activity, so was interesting to study.
  • 5.5. Transferase was compared with sialidase (external enzyme).
  • 6.6. Kinetics other than those already performed by us were undertaken in order to confirm its location.
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14.
  • 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.
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15.
  • 1.1. The purpose of this study was to determine whether biochemical changes of skeletal muscle that occur as a result of exercise in young rats persist into adulthood.
  • 2.2. Littermates (10 days old) were assigned to a 3, 6 and 12 week control or training group. In addition, a rest-exercise group (R-E) and exercise-rest (E-R) group were included.
  • 3.3. The rest-exercise and exercise-rest rats were maintained for the 12 weeks with the first 6 weeks being either rest or exercise and the condition reversed during the last 6 weeks of the experiment.
  • 4.4. Myofibril ATPase activity of rat plantaris increased from the 10d to 12 week animals (P < 0.05). As anticipated, training resulted in a lowered activity at 6 and 12 weeks compared to controls.
  • 5.5. The Ca2+ uptake and Ca2+-ATPase activity of the sarcoplasmic reticulum followed a similar pattern.
  • 6.6. With regard to the exercise-rest rats, the myofibril and SR ATPase activities at 12 weeks were comparable to the 12 weeks control rats.
  • 7.7. The rest-exercise group approximated the 12 week training group with regard to myofibril and SR ATPase activities (P > 0.05).
  • 8.8. The results suggest that the training adaptations that occur during development of skeletal muscle return to normal, when training ceases in the adult rat.
  • 9.9. Furthermore, animals that started to train prior to puberty do not have a greater capacity to adapt than animals which initiated training during adulthood.
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16.
  • 1.1. DNase-I-like activity occurs in the carp (Cyprinus carpio) liver cytosol (supernatant 105,000g).
  • 2.2. The enzyme resembles DNase I from bovine pancreas in respect to the molecular mass (~31 kDa), pH (7.4) and ion requirements (Mg2+, Ca2+) and the ability to degrade native as well as denatured DNA.
  • 3.3. As judged by comparison of DNase zymograms obtained after native- and SDS-PAGE, the enzyme occurs in the three molecular forms of similar molecular weight and different charges.
  • 4.4. All these forms are inhibited by rabbit skeletal muscle actin as well as by endogenous actin isolated from the carp liver cytosol.
  • 5.5. DNase from the carp liver cytosol does not interact with the antibodies directed against DNase I from bovine pancreas and against DNase I from the rat and bovine parotid glands.
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17.
  • 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 S0.5 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.
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18.
  • 1.1. A subcellular fractionation procedure for bovine adrenal glands was designed with the aim to study the biochemical properties of Ca2+ stores in chromaffin cells.
  • 2.2. The thapsigargin-sensitive compartment of Ca2+ stores was found to be highly enriched in a light microsomal fraction (LMF) on a 15–30% linear sucrose gradient, and was found to be essentially devoid of contamination by plasma, mitochondrial or secretory granule membranes.
  • 3.3. A Ca2+-pumping ATPase was identified in this LMF as a 97 kDa protein forming an acid-stable, Ca2+-dependent, thapsigargin-sensitive phosphorylated intermediate upon incubation with [γ-32P]ATP, suggesting this protein to represent a SERCA-3 isoform of Ca2+ ATPases.
  • 4.4. A major 162 kDa protein, previously demonstrated in the isolated chromaffin cells, was enriched in the LMF, distributing on sucrose gradients in parallel with the thapsigargin-sensitive Ca2+ uptake.
  • 5.5. LMF appears to represent a part of the thapsigargin-sensitive Ca2+ store of chromaffin cells, and should be useful for further studies of the store properties at the subcellular and molecular level.
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19.
  • 1.1. A method for purifying undischarged nematocysts from Hydra and other cnidarians is described.
  • 2.2. Isolated cysts (relative densities 1.22–1.24) evaginate their tubular content even after previous dehydration.
  • 3.3. The cyst wall is permeable to dyes of mol. wts up to 600,000.
  • 4.4. Approximately two-thirds of the cyst's dry wt are soluble proteins. Eighty per cent of them are of low mol. wt and highly anionic, presumably serving as binding sites for Ca2+ and Mg2+.
  • 5.5. The other 20% includes 30 different proteins amongst them toxins and enzymes (phospholipase and little proteases but no collagenase, chitinase or hyaluronidase).
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20.
  • 1.1. The incorporation of 32P into the contractile proteins of the anterior byssus retractor muscle of Mytilus edilus L. was analyzed during the different stages of a contraction-catch-relaxatin cycle.
  • 2.2. The experiments were performed with saponin-skinned fibers preincubated with γ-32P-ATP.
  • 3.3. The total amount of 32P incorporated into the fiber proteins was anlyzed by measuring the label of TCA-insoluble protein in a scintillation counter.
  • 4.4. The dose incorporated was about twice as high during Ca2+ induced contraction and serotonin induced accelerated relaxation as during test and catch.
  • 5.5. The molecular mass of the phosphorylated proteins was analyzed by autoradiography of the proteins separated by SDS-PAGE.
  • 6.6. Up to 26 protein spots of different molecular masses were labelled, including such well characterized protein spe+cies as myosin heavy and light chains, paramyosin and tropomyosin.
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