Sperm chemotaxis in siphonophores. II. Calcium-dependent asymmetrical movement of spermatozoa induced by the attractant

1984 ◽  
Vol 68 (1) ◽  
pp. 163-181
Author(s):  
M.P. Cosson ◽  
D. Carre ◽  
J. Cosson
Keyword(s):  
Calcium Ions ◽  
Calcium Concentration ◽  
Sea Water ◽  
Large Diameter ◽  
Chemotactic Response ◽  
Wide Area ◽  
Ionophore A23187 ◽  
Calcium Dependent ◽  
Sperm Chemotaxis ◽  
High Calcium

Spermatozoa from siphonophores have been shown to be attracted towards an extracellular structure, the cupule, which covers the predetermined site of fertilization of the egg. Observations on sperm behaviour during the chemotactic response show that spermatozoa describe trajectories of large diameter (700-1000 micron) while far from the cupule, and of smaller diameter (200 micron) in the cupule area. The transition between the two types of swimming occurs progressively when spermatozoa cross a 3 mm wide area around the cupule. After a few minutes 99% of the spermatozoa keep swimming around the attractant source, following circular paths 150–200 micron in diameter. In the absence of the attractant, comparable modifications of sperm trajectories are observed in the presence of the ionophore A23187 and high calcium concentrations. In the presence of 10(−2) M calcium ions, A23187-treated spermatozoa describe trajectories 200 micron in diameter, which increase up to 800 micron at lower calcium concentrations (10(−6) M). In the absence of calcium ions, spermatozoa swim across the cupule area without modification of their trajectories and no sperm accumulation can be detected. This requirement of the chemotactic response for calcium ions is observed either with fresh cupules stuck on the eggs, with cupules separated from the eggs, or with cupule extracts. Moreover, a soluble component fractionated from the cupule induces, when diluted in sea water, a reduction in the size of the sperm trajectories and this also requires calcium ions. The present data show that the chemotactic response of siphonophore sperm, which requires millimolar concentrations of calcium ions, occurs through a non-transient induction of increased asymmetry of the flagellar waveform. It is proposed that the natural attractant operates to produce an increase in the intraaxonemal calcium concentration.

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.

scholarly journals Modulation of thrombin-mediated activation of factor VIII:C by calcium ions, phospholipid, and platelets

Blood ◽  
1985 ◽  
Vol 66 (1) ◽  
pp. 53-58
Author(s):  
MB Hultin
Keyword(s):  
Calcium Ions ◽  
Calcium Concentration ◽  
Human Platelets ◽  
Ionophore A23187 ◽  
Factor X ◽  
Platelet Activity ◽  
Platelet Surface ◽  
New Finding ◽  
Factor X Activation ◽  
External Calcium

The activation of factor VIII:C by thrombin appears to be an important prerequisite for the function of factor VIII:C as a cofactor in factor X activation in coagulation. The possible modulation of factor VIII:C activation by potential cofactors such as calcium ions, phospholipid, and platelets was studied systematically. Factor VIII:C activation could not be studied in the complete absence of Ca2+, since factor VIII:C activity decayed rapidly in calcium-free buffers, EDTA, or ethylene glycol tetra-acetic acid (EGTA), with only partial or no recovery of activity after readdition of Ca2+, Mn2+, or Mg2+. Added calcium chloride at 1.25, 2.5, 4, 10, 50, and 200 mmol/L produced progressive inhibition of factor VIII:C activation, with complete inhibition achieved by 50 mmol/L. Crude phospholipid preparations gave varying results, while purified phospholipids either had no effect or inhibited activation. This paper reports the new finding that fresh washed human platelets markedly potentiated factor VIII:C activation by a low concentration of thrombin (0.02 U/mL), even with prostaglandin E1 (PGE1) or dibutyryl cyclic AMP (cAMP) added to the washed platelets. However, the activity of platelets in factor VIII:C activation was inhibited by inclusion of PGE1 or dibutyryl cAMP during platelet washing, and ionophore A23187 increased this platelet activity; these data suggest that platelet stimulation is involved in the development of this activity. When platelets were maximally stimulated by thrombin (0.5 U/mL), the external calcium concentration increased 55 to 160 mumol/L, as measured with murexide, supporting the possible modulation of factor VIII:C activation by a transient increase in Ca2+ at the platelet surface.

Interactions of methylxanthines, nonxanthine phosphodiesterase inhibitors, and calcium with morphine in the guinea pig myenteric plexus

1979 ◽  
Vol 57 (8) ◽  
pp. 853-859 ◽  
Author(s):  
Jana Sawynok ◽  
Khem Jhamandas
Keyword(s):  
Guinea Pig ◽  
Myenteric Plexus ◽  
Calcium Concentration ◽  
Longitudinal Muscle ◽  
Phosphodiesterase Inhibitors ◽  
Ionophore A23187 ◽  
Ach Release ◽  
Pde Inhibitors ◽  
High Calcium ◽  
High Calcium Concentration

In an earlier study, theophylline was shown to antagonize the morphine-induced inhibition of electrically induced contractions of the longitudinal muscle – myenteric plexus preparation from the guinea pig ileum. In the present study, acetylcholine (ACh) released from the myenteric plexus was measured directly using a radioenzymatic assay. Theophylline antagonized the morphine-induced inhibition of ACh release. A similar antagonism was also observed with caffeine and 3-isobutyl-1-methylxanthine (IBMX). All three methylxanthines also increased ACh release. The nonxanthine phosphodiesterase (PDE) inhibitors 4-(3-butoxy-4-methoxy)-2-imidazolidinone (Ro 20-1724) and 1-ethyl-4-isopropylidenehydrazino-1H-pyrozolo(3,4-b)-pyridine-5-carboxylate, ethylester, HCl (SQ 20,009) generally did not antagonize the morphine-induced inhibition of ACh release. The PDE inhibitor SQ 20,009, but not Ro 20-1724, enhanced the release of ACh. Both high calcium concentration and the divalent cation ionophore A23187 antagonized the inhibitory action of morphine on ACh release. These observations suggest that alteration in calcium fluxes rather than the inhibition of PDE mediate the methylxanthine-induced antagonism of morphine in this preparation.

scholarly journals Modulation of thrombin-mediated activation of factor VIII:C by calcium ions, phospholipid, and platelets

Blood ◽  
1985 ◽  
Vol 66 (1) ◽  
pp. 53-58 ◽  
Author(s):  
MB Hultin
Keyword(s):  
Calcium Ions ◽  
Calcium Concentration ◽  
Human Platelets ◽  
Ionophore A23187 ◽  
Factor X ◽  
Platelet Activity ◽  
Platelet Surface ◽  
New Finding ◽  
Factor X Activation ◽  
External Calcium

Abstract The activation of factor VIII:C by thrombin appears to be an important prerequisite for the function of factor VIII:C as a cofactor in factor X activation in coagulation. The possible modulation of factor VIII:C activation by potential cofactors such as calcium ions, phospholipid, and platelets was studied systematically. Factor VIII:C activation could not be studied in the complete absence of Ca2+, since factor VIII:C activity decayed rapidly in calcium-free buffers, EDTA, or ethylene glycol tetra-acetic acid (EGTA), with only partial or no recovery of activity after readdition of Ca2+, Mn2+, or Mg2+. Added calcium chloride at 1.25, 2.5, 4, 10, 50, and 200 mmol/L produced progressive inhibition of factor VIII:C activation, with complete inhibition achieved by 50 mmol/L. Crude phospholipid preparations gave varying results, while purified phospholipids either had no effect or inhibited activation. This paper reports the new finding that fresh washed human platelets markedly potentiated factor VIII:C activation by a low concentration of thrombin (0.02 U/mL), even with prostaglandin E1 (PGE1) or dibutyryl cyclic AMP (cAMP) added to the washed platelets. However, the activity of platelets in factor VIII:C activation was inhibited by inclusion of PGE1 or dibutyryl cAMP during platelet washing, and ionophore A23187 increased this platelet activity; these data suggest that platelet stimulation is involved in the development of this activity. When platelets were maximally stimulated by thrombin (0.5 U/mL), the external calcium concentration increased 55 to 160 mumol/L, as measured with murexide, supporting the possible modulation of factor VIII:C activation by a transient increase in Ca2+ at the platelet surface.

Inhibition of phospholipase A2 isoenzymes in human endometrium by mefenamic acid and indomethacin: modulation by calcium ions

1988 ◽  
Vol 119 (1) ◽  
pp. 141-145 ◽  
Author(s):  
R. C. Bonney ◽  
S. T. Qizilbash ◽  
S. Franks
Keyword(s):  
Phospholipase A2 ◽  
Calcium Ions ◽  
Mefenamic Acid ◽  
Calcium Concentration ◽  
Phospholipase A ◽  
Similar Relationship ◽  
Calcium Dependent ◽  
Phospholipase A2 Activity

ABSTRACT The inhibition of endometrial phospholipase A2 activity by the non-steroidal anti-inflammatory agents mefenamic acid and indomethacin was studied over the concentration range 1 mmol/l–0·1 μmol/l. Both phospholipase A2 type 1 (a calcium-dependent enzyme) and phospholipase A2 type 2 (a calciumindependent enzyme) were inhibited by mefenamic acid, but the magnitude of the inhibition was dependent on calcium concentration. Phospholipase A2 type 1 was inhibited 50% by 10 μmol mefenamic acid/1 in the presence of 1·25–5 mmol calcium/l, but a concentration of 2·2 mmol mefenamic acid/l was required for 50% inhibition in the absence of calcium. On the other hand, phospholipase A2 type 2 was inhibited 50% by 22 μmol mefenamic acid/1 in the absence of calcium and by 100 μmol mefenamic acid/l in the presence of calcium (2·5 mmol/l). Although indomethacin was a less effective inhibitor of phospholipase A2 activity, a similar relationship with calcium was demonstrated. However, indomethacin also had a stimulatory effect on phospholipase A2 type 1 activity in the absence of calcium. Our findings suggest that the two endometrial enzymes may be inhibited by different mechanisms and that the dependence of the enzyme on calcium for activation may be a contributing factor. J. Endocr. (1988) 119, 141–145

scholarly journals Effect of increased calcium concentration in sea water on calcification and photosynthesis in the scleractinian coral Galaxea fascicularis

2002 ◽  
Vol 205 (14) ◽  
pp. 2107-2113 ◽  
Author(s):  
Alan T. Marshall ◽  
Peta L. Clode
Keyword(s):  
Calcium Carbonate ◽  
Respiration Rate ◽  
Scleractinian Coral ◽  
Calcium Concentration ◽  
Sea Water ◽  
Oxygen Production ◽  
Amorphous Calcium Carbonate ◽  
High Calcium ◽  
Photosynthetic Oxygen ◽  
The Relationship

SUMMARY The relationship between calcification and photosynthesis in coral was investigated using standard sea water with enhanced calcium concentration. In standard sea water at 23°C with the calcium concentration increased by 2.5 mmol l-1, incorporation of calcium into the skeleton increased by 30-61 %, depending on the method of data normalisation, and photosynthesis, measured as 14C incorporation into the tissues, also increased by 87 %. At 29 °C, calcium incorporation into the skeleton increased by 54-84 % and 14C incorporation increased by 32 % when sea water calcium concentration was increased by 5 mmol l-1. However, photosynthesis measured as net photosynthetic oxygen production did not increase. Similarly there was no change in respiration rate when coral polyps were incubated in high-calcium sea water. It is conjectured that an increase in photorespiration may be responsible for the latter observations. Bisphosphonate has been considered to inhibit calcification but not photosynthesis in corals. We show that bisphosphonate may not inhibit formation of amorphous calcium carbonate and that the inhibition of calcification is possibly illusory. The data are consistent with the trans-calcification model, which suggests that calcification is a source of CO2 for photosynthesis in corals.

scholarly journals Cellular pathways of calcium transport and concentration towards mineral formation in sea urchin larvae

2020 ◽  
Author(s):  
Keren Kahil ◽  
Neta Varsano ◽  
Andrea Sorrentino ◽  
Eva Pereiro ◽  
Peter Rez ◽  
...  
Keyword(s):  
Sea Urchin ◽  
Calcium Ions ◽  
Calcium Concentration ◽  
Sea Water ◽  
Coordination Shell ◽  
Water Levels ◽  
Main Peak ◽  
Amorphous Calcium Carbonate ◽  
X Ray ◽  
Wide Range

AbstractSea urchin larvae have an endoskeleton consisting of two calcitic spicules. The primary mesenchyme cells (PMCs) are the cells that are responsible for spicule formation. PMCs endocytose sea water from the larval internal body cavity into a network of vacuoles and vesicles, where calcium ions are concentrated until they precipitate in the form of amorphous calcium carbonate (ACC). The mineral is subsequently transferred to the syncytium, where the spicule forms. Using cryo-soft X-ray microscopy (cryo-SXM) we imaged intra-cellular calcium-containing particles in the PMCs and acquired Ca-L2,3 X-ray absorption near edge spectra (XANES) of these Ca-particles. Using the pre-peak/main peak (L2’/ L2) intensity ratio, which reflects the atomic order in the first Ca coordination shell, we determined the state of the calcium ions in each particle. The concentration of Ca in each of the particles was also determined by the integrated area in the main Ca absorption peak. We observed about 700 Ca-particles with order parameters, L2’/ L2, ranging from solution to hydrated and anhydrous ACC, and with concentrations ranging between 1-15 M. We conclude that in each cell the calcium ions exist in a continuum of states. This implies that most, but not all water, is expelled from the particles. This cellular process of calcium concentration may represent a widespread pathway in mineralizing organisms.SignificanceOrganisms form mineralized skeletons, many of which are composed of calcium salts. Marine organisms extract calcium ions from sea water. One of the main unresolved issues is how organisms concentrate calcium by more than 3 orders of magnitude, to achieve mineral deposition in their skeleton. Here we determine the calcium state in each of the calcium-containing vesicles inside the spicule-building cells of sea urchin larvae. We show that within one cell there is a wide range of concentrations and states from solution to solid. We hypothesize that calcium concentration increases gradually in each vesicle, starting from sea water levels and until mineral is deposited. This model might well be relevant to other phyla, thus advancing the understanding of biomineralization processes.

scholarly journals Acetylcholine and Calcium on Membrane Permeability and Contraction of Intestinal Smooth Muscle

1967 ◽  
Vol 50 (5) ◽  
pp. 1157-1172 ◽  
Author(s):  
Leon Hurwitz ◽  
Stanley Von Hagen ◽  
Paul D. Joiner
Keyword(s):  
Calcium Ions ◽  
Calcium Concentration ◽  
Mechanical Response ◽  
Muscle Tone ◽  
Extracellular Calcium ◽  
Storage Site ◽  
Bathing Medium ◽  
Potassium Efflux ◽  
High Calcium ◽  
Low Levels

Acetylcholine elicited a sustained contraction and an increase in potassium efflux in longitudinal muscle isolated from the guinea pig ileum. Stepwise increases in the calcium concentration of the bathing medium, from 0.06 to 36 mM generally reduced the increase in potassium efflux, but had a complex effect on the mechanical response. Contractions produced by high levels of acetylcholine became progressively larger or remained at a high magnitude as the calcium concentration was increased. Contractions produced by low levels of acetylcholine also improved initially, but were depressed again by the highest concentration of calcium introduced. Ethanol, in the appropriate concentration, inhibited completely the acetylcholine-induced contraction without reducing the increase in potassium efflux. Calcium reversed this effect. Both extracellular calcium and ethanol depressed the large, transient increase in muscle tone developed by fibers that were preincubated in a high calcium medium and then exposed to a calcium-free medium. These findings suggested that extracellular calcium ions react with two different sites in the membrane, a stabilizing site and a storage site. A muscle contraction is activated by calcium ions which diffuse from the storage site to the myoplasm. Calcium ions reacting with the stabilizing site impede this diffusion process. Part of the stimulatory effect of acetylcholine is derived from its capacity to counteract the action of calcium at the stabilizing site.

scholarly journals Mirolase, a novel subtilisin-like serine protease from the periodontopathogen Tannerella forsythia

2015 ◽  
Vol 396 (3) ◽  
pp. 261-275 ◽  
Author(s):  
Miroslaw Ksiazek ◽  
Abdulkarim Y. Karim ◽  
Danuta Bryzek ◽  
Jan J. Enghild ◽  
Ida B. Thøgersen ◽  
...  
Keyword(s):  
Serine Protease ◽  
Calcium Ions ◽  
Enzyme Stability ◽  
Amidolytic Activity ◽  
Tannerella Forsythia ◽  
Calcium Dependent ◽  
Genes Encoding ◽  
Mature Enzyme ◽  
Almost All ◽  
Unique Mechanism

Abstract The genome of Tannerella forsythia, an etiological factor of chronic periodontitis, contains several genes encoding putative proteases. Here, we characterized a subtilisin-like serine protease of T. forsythia referred to as mirolase. Recombinant full-length latent promirolase [85 kDa, without its signal peptide (SP)] processed itself through sequential autoproteolytic cleavages into a mature enzyme of 40 kDa. Mirolase latency was driven by the N-terminal prodomain (NTP). In stark contrast to almost all known subtilases, the cleaved NTP remained non-covalently associated with mirolase, inhibiting its proteolytic, but not amidolytic, activity. Full activity was observed only after the NTP was gradually, and fully, degraded. Both activity and processing was absolutely dependent on calcium ions, which were also essential for enzyme stability. As a consequence, both serine protease inhibitors and calcium ions chelators inhibited mirolase activity. Activity assays using an array of chromogenic substrates revealed that mirolase specificity is driven not only by the substrate-binding subsite S1, but also by other subsites. Taken together, mirolase is a calcium-dependent serine protease of the S8 family with the unique mechanism of activation that may contribute to T. forsythia pathogenicity by degradation of fibrinogen, hemoglobin, and the antimicrobial peptide LL-37.

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