How calcium may cause exocytosis in sea urchin eggs

1987 ◽  
Vol 7 (5) ◽  
pp. 383-397 ◽  
Author(s):  
Michael Whitaker
Keyword(s):  
Membrane Fusion ◽  
Lipid Bilayers ◽  
Secretory Granule ◽  
Sea Urchin ◽  
Surface Potential ◽  
Membrane Lipids ◽  
Electrical Potential ◽  
Sea Urchin Eggs ◽  
Granule Membrane

The process of secretory granule-plasma membrane fusion can be studied in sea urchin eggs. Micromolar calcium concentrations are all that is required to bring about exocytosis in vitro. I discuss recent experiments with sea urchin eggs that concentrate on the biophysical aspects of granule-membrane fusion. The backbone of biological membranes is the lipid bilayer. Sea urchin egg membrane lipids have negatively charged head groups that give rise to an electrical potential at the bilayer-water interface. We have found that this surface potential can affect the calcium required for exocytosis. Effects on the surface potential may also explain why drugs like trifluoperazine and tetracaine inhibit exocytosis: they absorb to the bilayer and reduce the surface potential. The membrane lipids may also be crucial to the formation of the exocytotic pore through which the secretory granule contents are released. We have measured calcium-induced production of the lipid, diacylglycerol. This lipid can induce a phase transition that will promote fusion of apposed lipid bilayers. The process of exocytosis involves the secretory granule core as well as the lipids of the membrane. The osmotic properties of the granule contents lead to swelling of the granule during exocytosis. Swelling promotes the dispersal of the contents as they are extruded through the exocytotic pore. The movements of water and ions during exocytosis may also stabilize the transient fusion intermediate and consolidate the exocytotic pore as fusion occurs.

Cytasters induced within unfertilized sea-urchin eggs

1983 ◽  
Vol 61 (1) ◽  
pp. 175-189
Author(s):  
R. Kuriyama ◽  
G.G. Borisy
Keyword(s):  
Electron Microscopy ◽  
Sea Urchin ◽  
Sea Water ◽  
Light And Electron Microscopy ◽  
Sea Urchin Eggs ◽  
Microtubule Organizing Centres ◽  
Treatment Step

Conditions that induce the formation of asters in unfertilized sea-urchin eggs have been investigated. Monasters were formed by treatment of eggs with acidic or basic sea-water, or procaine- or thymol-containing sea-water. A second treatment step, incubation with D2O-containing, ethanol-containing or hypertonic sea-water induced multiple cytasters. The number and size of cytasters varied according to the concentration of agents and duration of the first and second treatments, and also upon the species of eggs and the season in which the eggs were obtained. Generally, a longer second treatment or a higher concentration of the second medium resulted in a higher number of cytasters per egg. Asters were isolated and then examined by light and electron microscopy. Isolated monasters apparently lacked centrioles, whereas cytasters obtained from eggs undergoing the two-step treatment contained one or more centrioles. Up to eight centrioles were seen in a single aster; the centrioles appeared to have been produced during the second incubation. Centrospheres prepared from isolated asters retained the capacity to nucleate the formation of microtubules in vitro as assayed by light and electron microscopy. Many microtubules radiated from the centre of isolated asters, whether they contained centrioles or not. This observation is consistent with many other reports that microtubule-organizing centres need not contain centrioles.

scholarly journals Phosphoprotein inhibition of calcium-stimulated exocytosis in sea urchin eggs.

1991 ◽  
Vol 113 (4) ◽  
pp. 769-778 ◽  
Author(s):  
T Whalley ◽  
I Crossley ◽  
M Whitaker
Keyword(s):  
Sea Urchin ◽  
Okadaic Acid ◽  
Cortical Granule ◽  
Granule Exocytosis ◽  
Sea Urchin Eggs ◽  
Transduction Mechanisms ◽  
Egg Signal ◽  
Cortical Granule Exocytosis ◽  
Gamma S

We have investigated the role of protein phosphorylation in the control of exocytosis in sea urchin eggs by treating eggs with a thio-analogue of ATP. ATP gamma S (adenosine 5'-O-3-thiotriphosphate) is a compound which can be used as a phosphoryl donor by protein kinases, leading to irreversible protein thiophosphorylation (Gratecos, D., and E.H. Fischer. 1974. Biochem. Biophys. Res. Commun. 58:960-967). Microinjection of ATP gamma S inhibits cortical granule exocytosis, but has no effect on the sperm-egg signal transduction mechanisms which normally cause exocytosis by generating an increase in [Ca2+]i. ATP gamma S requires cytosolic factors for its inhibition of cortical granule exocytosis: it does not affect exocytosis when applied directly to the isolated exocytotic apparatus. Our data suggest that ATP gamma S irreversibly inhibits exocytosis via thiophosphorylation of proteins associated with the egg cortex. We have identified two thiophosphorylated proteins (33 and 27 kD) that are associated with the isolated exocytotic apparatus. They may mediate the inhibition of exocytosis by ATP gamma S. In addition, we show that okadaic acid, an inhibitor of phosphoprotein phosphatases, prevents cortical granule exocytosis at fertilization without affecting calcium mobilization. Like ATP gamma S, okadaic acid has no effect on exocytosis in vitro. Our results suggest that an inhibitory phosphoprotein can obstruct calcium-stimulated exocytosis in sea urchin eggs; on the other hand, they do not readily support the idea that a protein phosphatase is an essential component of the mechanism controlling exocytosis.

Control of Exocytosis in Single Cells

Physiology ◽  
1989 ◽  
Vol 4 (2) ◽  
pp. 53-56 ◽  
Author(s):  
Y Maruyama
Keyword(s):  
Membrane Fusion ◽  
G Proteins ◽  
Secretory Granule ◽  
Single Cells ◽  
Guanine Nucleotide ◽  
Signal Transducers ◽  
Granule Membrane ◽  
Guanine Nucleotide Binding ◽  
Nucleotide Binding Proteins ◽  
Guanine Nucleotide Binding Proteins

Exocytosis can be quantified by measuring changes in membrane capacitance in single internally perfused cells. Exocytosis is controlled by guanine nucleotide-binding proteins (G proteins) acting as key signal transducers. Different G proteins mediate receptor signaling and secretory granule-membrane fusion.

Ionic and permeability requirements for exocytosis in vitro in sea urchin eggs

1988 ◽  
Vol 101 (1) ◽  
pp. 199-207 ◽  
Author(s):  
Joshua Zimmerberg ◽  
Jessica Liu
Keyword(s):  
Sea Urchin ◽  
Sea Urchin Eggs

A fluorescence dequenching method for monitoring exocytotic membrane fusion in fertilization of single sea urchin eggs

1999 ◽  
Vol 91 (1) ◽  
pp. 5-15
Author(s):  
Kazuhisa Takemoto ◽  
Ken-ichi Hirano ◽  
Tsuyoshi Hayakawa ◽  
Ritsu Kuroda ◽  
Hideyo Kuroda
Keyword(s):  
Membrane Fusion ◽  
Sea Urchin ◽  
Sea Urchin Eggs ◽  
Fluorescence Dequenching

scholarly journals Fengycin induces ion channels in lipid bilayers mimicking target fungal cell membranes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Anastasiia A. Zakharova ◽  
Svetlana S. Efimova ◽  
Valery V. Malev ◽  
Olga S. Ostroumova
Keyword(s):  
Ion Channels ◽  
Lipid Bilayers ◽  
Cell Membranes ◽  
Membrane Lipids ◽  
Electrical Potential ◽  
Membrane Conductance ◽  
Pressure Profile ◽  
Molecular Shape ◽  
Bathing Solution ◽  
Fungal Cell

Abstract The one-sided addition of fengycin (FE) to planar lipid bilayers mimicking target fungal cell membranes up to 0.1 to 0.5 μM in the membrane bathing solution leads to the formation of well-defined and well-reproducible single-ion channels of various conductances in the picosiemens range. FE channels were characterized by asymmetric conductance-voltage characteristic. Membranes treated with FE showed nonideal cationic selectivity in potassium chloride bathing solutions. The membrane conductance induced by FE increased with the second power of the lipopeptide aqueous concentration, suggesting that at least FE dimers are involved in the formation of conductive subunits. The pore formation ability of FE was not distinctly affected by the molecular shape of membrane lipids but strongly depended on the presence of negatively charged species in the bilayer. FE channels were characterized by weakly pronounced voltage gating. Small molecules known to modify the transmembrane distribution of electrical potential and the lateral pressure profile were used to modulate the channel-forming activity of FE. The observed effects of membrane modifiers were attributed to changes in lipid packing and lipopeptide oligomerization in the membrane.

scholarly journals Single-molecule FRET study of SNARE-mediated membrane fusion

2011 ◽  
Vol 31 (6) ◽  
pp. 457-463 ◽  
Author(s):  
Jiajie Diao ◽  
Yuji Ishitsuka ◽  
Woo-Ri Bae
Keyword(s):  
Membrane Fusion ◽  
Lipid Bilayers ◽  
Single Molecule ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Cellular Processes ◽  
Single Molecule Fret ◽  
Protein Receptor ◽  
Hydrophobic Cores

Membrane fusion is one of the most important cellular processes by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure. Proteins, called SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor), play a central role in the fusion process that is also regulated by several accessory proteins. In order to study the SNARE-mediated membrane fusion, the in vitro protein reconstitution assay involving ensemble FRET (fluorescence resonance energy transfer) has been used over a decade. In this mini-review, we describe several single-molecule-based FRET approaches that have been applied to this field to overcome the shortage of the bulk assay in terms of protein and fusion dynamics.

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