The induction of the acrosome reaction in guinea-pig sperm by the divalent metal cation ionophore A23187

1978 ◽  
Vol 32 (1) ◽  
pp. 137-151
Author(s):  
D.P. Green
Keyword(s):  
Guinea Pig ◽  
Metal Cation ◽  
Acrosome Reaction ◽  
Divalent Metal ◽  
Secretory Cells ◽  
Free Calcium ◽  
Ionophore A23187 ◽  
Divalent Metal Cation ◽  
Free Calcium Concentration ◽  
External Calcium

The divalent metal cation ionophore A23187 induces an acrosome reaction in guinea-pig sperm which is dependent on external calcium. Examination of this acrosome reaction by electron microscopy shows that it is morphologically normal. The known properties of A23187 and the morphological similarity between the acrosome reaction and the secretory discharges of other secretory cells suggests that the immediate cause of the acrosome reaction is an increase in the cytoplasmic free calcium concentration.

The activation of proteolysis in the acrosome reaction of guinea-pig sperm

1978 ◽  
Vol 32 (1) ◽  
pp. 153-164
Author(s):  
D.P. Green
Keyword(s):  
Guinea Pig ◽  
Acrosome Reaction ◽  
Morphological Changes ◽  
Divalent Metal ◽  
Free Calcium ◽  
Ionophore A23187 ◽  
Reaction Proceeds ◽  
Insoluble Form ◽  
Acrosin Activity ◽  
Sperm Population

The divalent metal cation ionophore A23187 rapidly induces a normal acrosome reaction in a population of guinea-pig sperm suspended in calcium medium. In the course of the acrosome reaction, proacrosin, the zymogen precursor of the protease acrosin, is activated. Although the acrosome reaction causes exocytosis of the acrosomal contents, ‘soluble’ acrosin is not released in significant amounts until well after the sperm population as a whole has undergone an acrosome reaction. This suggests that proacrosin is stored within the acrosome in an insoluble form and that exocytosis of the acrosomal contents in the acrosome reaction is insufficient, by itself, to cause its immediate dissolution. Electron micrographs of sperm undergoing an A23187-induced acrosome reaction in the presence of the acrosin inhibitors benzamidine, p-amino-benzamidine and phenylmethylsulphonyl fluoride show that the acrosome reaction proceeds normally but that dispersal of the acrosomal contents is inhibited. These morphological changes are, for the most part, below the limit of resolution of the light microscope and using light microscopy to assess whether an acrosome reaction has taken place, it can be mistakenly inferred that the reaction itself is inhibited by the acrosin inhibitors. The inhibition of the dispersal of the acrosomal contents by acrosin inhibitors suggests that acrosin activity is important in solubilizing acrosin. These experimental observations, taken with the evidence that the acrosome reaction is a response to an increase in intracellular free calcium, have been taken as the basis of a proposal for the mechanism of proacrosin activation in the acrosome reaction.

scholarly journals Role of the divalent metal cation in the pyruvate oxidase reaction.

1982 ◽  
Vol 257 (16) ◽  
pp. 9605-9611
Author(s):  
R Blake ◽  
T A O'Brien ◽  
R B Gennis ◽  
L P Hager
Keyword(s):  
Metal Cation ◽  
Divalent Metal ◽  
Pyruvate Oxidase ◽  
Divalent Metal Cation ◽  
Oxidase Reaction

Cholinergic effects on intracellular free calcium concentration in renal corpuscle: role of parietal sheet

1992 ◽  
Vol 262 (2) ◽  
pp. F248-F255
Author(s):  
F. Lebrun ◽  
F. Morel ◽  
G. Vassent ◽  
J. Marchetti
Keyword(s):  
Calcium Release ◽  
Intracellular Free Calcium ◽  
Free Calcium ◽  
Response Curves ◽  
Glomerular Function ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration ◽  
External Calcium ◽  
Cholinergic Effects

To investigate a possible effect of cholinergic agonists on the renal glomerular function, fura-2 microfluorometric measurements of intracellular free calcium [( Ca2+]i) were performed on single intact glomeruli, single isolated parietal sheets of the Bowman's capsule and single parietal sheet-deprived glomeruli (PS-D glomerulus). Carbachol (10(-4) M), in the presence of 2 mM external calcium, induced a biphasic increase in [Ca2+]i characterized by a sharp initial peak followed by a sustained plateau in the whole glomerulus (delta [Ca2+]i = 177 +/- 13 and 70 +/- 7 nM, respectively; n = 21) and in the parietal sheet (418 +/- 30 and 111 +/- 13 nM, respectively; n = 21). In the PS-D glomerulus (n = 9), the response was less marked and included a barely visible peak (77 +/- 13 nM) and a relatively low plateau (49 +/- 11 nM). In the absence of external calcium, the peak phase was preserved in the three structures, indicating a calcium release from intracellular pools, whereas the plateau, due to the entry of external calcium, was suppressed. These effects were fully inhibited by 10(-4) M of either atropine or pirenzepine, demonstrating the muscarinic nature of the receptors. Dose-response curves showed that the parietal sheet was more sensitive to the physiological agonist (acetylcholine) than to carbachol. A still unexplained difference in sensitivity was noted between peak and plateau, respectively (half-maximal responses were 5 x 10(-6) vs. 5 x 10(-7) M for carbachol and 2 x 10(-7) vs. 3 x 10(-8) M for acetylcholine).(ABSTRACT TRUNCATED AT 250 WORDS)

Divalent metal cation requirements of phosphofructokinase-2 from E. coli. Evidence for a high affinity binding site for Mn2+

2011 ◽  
Vol 505 (1) ◽  
pp. 60-66 ◽  
Author(s):  
Jaime Andrés Rivas-Pardo ◽  
Andrés Caniuguir ◽  
Christian A.M. Wilson ◽  
Jorge Babul ◽  
Victoria Guixé
Keyword(s):  
Binding Site ◽  
Metal Cation ◽  
Divalent Metal ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
Divalent Metal Cation ◽  
E Coli ◽  
High Affinity ◽  
High Affinity Binding Site

scholarly journals The effect of permeant and impermeant osmoticants on exocytosis in guinea pig sperm

1991 ◽  
Vol 100 (4) ◽  
pp. 761-769
Author(s):  
D.P. Green
Keyword(s):  
Electron Microscopy ◽  
Guinea Pig ◽  
Membrane Fusion ◽  
Acrosome Reaction ◽  
Ammonium Acetate ◽  
Ammonium Acetate Solution ◽  
Acetate Solution ◽  
Normal Medium ◽  
Acrosomal Membrane ◽  
External Calcium

Guinea pig sperm were suspended in calcium-containing medium supplemented with various concentrations of the tetrasaccharide, stachyose. At concentrations up to and including 0.6 M, stachyose was without effect on the A23187-induced acrosome reaction. At 1.0 M stachyose, greater than 97% of sperm retained their acrosome after exposure to A23187, as judged by light microscopy. Electron microscopy demonstrated, however, that exocytotic membrane fusion had occurred, although with substantial retention of the acrosomal matrix. Sperm incubated in 1.0 M stachyose solutions also underwent exocytotic membrane fusion in the absence of A23187 and external calcium. Sperm suspended in 0.175 M ammonium chloride solution progressively lost motility over 30 min, but without acrosomal swelling. By contrast, sperm in 0.19 M ammonium acetate underwent substantial swelling of the acrosome within 2–5 min. 70–80% of these sperm were able to exclude the vital dye propidium iodide with their acrosomes swollen. These sperm underwent acrosomal shrinkage if resuspended in normal medium within 5–10 min, and the majority (60–70%) recovered some motility. These sperm could undergo an A23187-induced acrosome reaction. Electron microscopy indicated that swelling in ammonium acetate solution solubilizes much of the acrosomal matrix and causes internal fusion between adjacent regions of the outer acrosomal membrane. There was no exocytotic membrane fusion in ammonium acetate solution, however. The evidence suggests that there is no stachyose osmolality for guinea pig sperm which will suppress the membrane fusion associated with exocytosis, and that sufficiently high osmolalities cause exocytotic membrane fusion in the absence of calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

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