scholarly journals Transport of Ca2+ and Na+ across the chromaffin-granule membrane

1981 ◽  
Vol 200 (1) ◽  
pp. 99-107 ◽  
Author(s):  
J H Phillips
Keyword(s):  
Plasma Membrane ◽  
Exchange Reaction ◽  
Osmotic Shock ◽  
Ruthenium Red ◽  
Chromaffin Granule ◽  
Inner Surface ◽  
Granule Membrane ◽  
Chromaffin Granule Ghosts ◽  
Kinetics Of ◽  
Entry Mechanism

Bovine chromaffin-granule ghosts accumulate 45Ca2+ in a temperature- and osmotic-shock-sensitive process; the uptake is saturable, with Km 38 microM and Vmax. 28 nmol/min per mg at 37 degrees C. Entry occurs by exchange with Ca2+ bound to the inner surface of the membrane. It is inhibited non-competitively by Na+, La3+ and Ruthenium Red (Ki 10.7 mM, 7 microM and 2 microM respectively), and competitively by Mg2+ (ki 0.9 mM). Uptake was not stimulated by ATP. Na+ induces Ca2+ efflux; Ca2+ can re-enter the ghosts by a process of Ca2+/Na+ exchange. La3+ inhibits Ca2+ efflux during Ca2+-exchange, and Ca2+ efflux induced by Na+, suggesting that Ca2+ uptake and efflux, and Ca2+/Na+ exchange, are catalysed by the same protein. Na+ enters ghosts during CA2+ efflux, but the kinetics of its entry are not exactly similar to the kinetics of Ca2+ efflux. Initially 1-2 Na+ enter per Ca2+ lost, but at equilibrium 3-4 Na+ have replaced each Ca2+. There is no evidence that either Ca2+ uptake or efflux by Ca2+/Na+ exchange is electrogenic, suggesting that the stoichiometry of exchange is Ca2+/2Na+. This exchange reaction may have a role in depleting cytoplasmic Ca2+ after depolarization-induced Ca2+ entry through the adrenal medulla plasma membrane; there is some evidence that there may be an additional entry mechanism for Na+ across the granule membrane.

scholarly journals Reduction of membrane-bound dopamine β-hydroxylase from the cytoplasmic surface of the chromaffin-granule membrane

1982 ◽  
Vol 202 (3) ◽  
pp. 759-770 ◽  
Author(s):  
M Grouselle ◽  
J H Phillips
Keyword(s):  
Accumulation Rate ◽  
Chromaffin Granule ◽  
Cytoplasmic Surface ◽  
Dopamine Beta Hydroxylase ◽  
Matrix Surface ◽  
The Matrix ◽  
Granule Membrane ◽  
Membrane Bound ◽  
Chromaffin Granule Ghosts ◽  
Low Ionic Strength

Resealed bovine chromaffin-granule ‘ghosts’ were used for assaying the membrane-bound form of dopamine beta-hydroxylase. Hydroxylation of the substrate tyramine is dependent on its accumulation within the ‘ghosts’, where the active site of the enzyme is located. Free tyramine in the medium is at a low concentration, low ionic strength and a relatively high pH (7.0), so that even in the presence of a reducing agent (co-reductant) the unaccumulated amine is hydroxylated at a negligible rate. ‘Ghosts’ contain an endogenous co-reductant, which is shown to be catecholamine remaining in the membrane itself after granule lysis. Catecholamine that is free in solution in the medium or in the interior of the ‘ghosts’ is not effective as co-reductant, nor is ascorbate, in contrast with the situation with soluble dopamine beta-hydroxylase. Ferrocyanide is an active co-reductant, however, giving a hydroxylation rate approximately equal to the tyramine accumulation rate: it does not enter the ‘ghosts’, nor does the enzyme appear to utilize ferrocyanide sealed inside the ‘ghosts’. A mechanism must therefore exist for transferring electrons across the membrane from the cytoplasmic surface to the matrix surface. NADH is not an electron donor for the enzyme, nor is cytochrome b-561 involved.

scholarly journals Hydroxytryptamine transport by the bovine chromaffin-granule membrane

1978 ◽  
Vol 170 (3) ◽  
pp. 673-679 ◽  
Author(s):  
J H Phillips
Keyword(s):  
Low Ph ◽  
Ph Gradient ◽  
Chromaffin Granule ◽  
Concentration Gradients ◽  
Granule Membrane ◽  
Chromaffin Granule Ghosts

5-Hydroxytryptamine is accumulated by resealed chromaffin-granule ‘ghosts’ if a pH gradient (acid inside) is imposed across their membranes by preincubating them at low pH. This uptake, like that driven by MgATP, is reserpine- and uncoupler-sensitive. This strongly suggests that catecholamines are taken up by intact granules in response to a pH gradient. In line with this, it is shown that 5-hydroxytryptamine decreases the pH gradient generated in the presence of MgATP, an effect that is inhibited by reserpine; nigericin, which discharges the pH gradient in the presence of K+, inhibits uptake. Permeant anions, however, also inhibit uptake. It is suggested that this may be because they permit equilibration of amine cations directly across the membrane, down concentration gradients.

scholarly journals VAMP2 and synaptotagmin mobility in chromaffin granule membranes: implications for regulated exocytosis

2021 ◽  
Author(s):  
Prabhodh S. Abbineni ◽  
Joseph S. Briguglio ◽  
Edwin R. Chapman ◽  
Ronald W. Holz ◽  
Daniel Axelrod
Keyword(s):  
Plasma Membrane ◽  
Optical Resolution ◽  
Chromaffin Granule ◽  
Diffusion Parameters ◽  
Bright Flash ◽  
Diffusion Characteristics ◽  
Granule Membrane ◽  
Synaptotagmin 1 ◽  
Glass Interface ◽  
Time Required

Granule-plasma membrane docking and fusion can only occur when proteins that enable these reactions are present at the granule-plasma membrane contact. Thus, the mobility of granule membrane proteins may influence docking, and membrane fusion. We measured the mobility of vesicle associated membrane protein 2 (VAMP2), synaptotagmin 1 (Syt1), and synaptotagmin 7 (Syt7) in chromaffin granule membranes in living chromaffin cells. We used a method that is not limited by standard optical resolution. A bright flash of strongly decaying evanescent field produced by total internal reflection (TIR) was used to photobleach GFP-labeled proteins in the granule membrane. Fluorescence recovery occurs as unbleached protein in the granule membrane distal from the glass interface diffuses into the more bleached proximal regions, enabling the measurement of diffusion coefficients. We found that VAMP2-EGFP and Syt7-EGFP are mobile with a diffusion coefficient of approximately 3 × 10-10 cm2/s. Syt1-EGFP mobility was below the detection limit. Utilizing these diffusion parameters, we estimated the time required for these proteins to arrive at docking and nascent fusion sites to be many tens of milliseconds. Our analyses raise the possibility that the diffusion characteristics of VAMP2 and Syt proteins could be a factor that influences the rate of exocytosis.

Kinetics of high-affinity Ca2+ sequestration in permeabilized rat pancreatic acini

1988 ◽  
Vol 254 (5) ◽  
pp. C621-C627 ◽  
Author(s):  
T. W. Hurley
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
Initial Rate ◽  
Ruthenium Red ◽  
Ionophore A23187 ◽  
Pancreatic Acini ◽  
High Affinity ◽  
Energy Dependent ◽  
Kinetics Of

Energy-dependent subcellular Ca2+ sequestration was studied in the presence of ruthenium red using rat pancreatic acini, which had been permeabilized by exposure to medium nominally free of Ca2+. The initial rate of Ca2+ uptake (approximately 2,800 pmol.min-1.mg acinar protein-1) quickly slowed, and a mean steady-state Ca2+ content of approximately 3,000 pmol/mg was reached after 5-10 min of incubation at 37 degrees C. Ca2+ uptake was stimulated by submicromolar Ca2+ concentrations (K0.5 = 156 nM); required Mg2+-ATP (K0.5 = 0.78 mM) was greatest at a pH of 7.0 and was abolished by the Ca2+ ionophore A23187. Other nucleotide phosphates as well as p-nitrophenylphosphate were relatively poor substrates, supporting Ca2+ uptake at initial rates that were 6-14% of those measured in the presence of ATP. These results show that pancreatic acini permeabilized without detergents possess a nonmitochondrial Ca2+ transporting system not located in the plasma membrane but with the properties expected of a major regulator of acinar cytosolic Ca2+ concentration.

scholarly journals Inhibition of adenosine triphosphatase, 5-hydroxytryptamine transport and proton-translocation activities of resealed chromaffin-granule ‘ghosts’

1980 ◽  
Vol 190 (2) ◽  
pp. 273-282 ◽  
Author(s):  
David K. Apps ◽  
James G. Pryde ◽  
Raul Sutton ◽  
John H. Phillips
Keyword(s):  
Molecular Weight ◽  
Atpase Activity ◽  
Adenosine Triphosphatase ◽  
Proton Translocation ◽  
Low Molecular Weight ◽  
Chromaffin Granule ◽  
Low Concentrations ◽  
Tributyltin Chloride ◽  
Granule Membrane ◽  
Chromaffin Granule Ghosts

1. Highly purified resealed chromaffin-granule ‘ghosts’ were assayed for ATPase and ATP-driven H+-translocation and 5-hydroxytryptamine-uptake activities, and for 5-hydroxytryptamine uptake driven by an imposed transmembrane H+-gradient. The effects of several inhibitors on these activities were studied. 2. Dicyclohexylcarbodi-imide inhibits all of these activities, but not in parallel; at low concentrations it decreases the permeability of the membrane to protons. 3. 4-Chloro-7-nitrobenzofuran (Nbf-Cl) and silicotungstate inhibit ATP-dependent activities, without effect on 5-hydroxytryptamine uptake driven by an imposed H+-gradient. 4. Tributyltin chloride inhibits all of the activities. 5. Treatment of the ‘ghosts’ with low concentrations of urea inhibits 5-hydroxytryptamine uptake and ATP-dependent generation of a transmembrane H+-gradient, without inhibiting ATPase activity. 6. Nbf-Cl and silicotungstate are without effect on the rate of leakage of 5-hydroxytryptamine from preloaded ‘ghosts’, whereas dicyclohexylcarbodi-imide and tributyltin chloride accelerate the rate of leakage. 7. Treatment of the membranes with 14C-labelled Nbf-Cl labels several proteins; membranes treated with dicyclohexyl[14C]carbodi-imide are labelled predominantly in a protein of low molecular weight, which may be analogous to the mitochondrial H+-conducting proteolipid. 8. It is concluded that Nbf-Cl and silicotungstate inhibit the H+-translocating ATPase of the granule membrane; that dicyclohexylcarbodi-imide inhibits the ATPase, and inhibits 5-hydroxytryptamine accumulation by accelerating leakage of the amine; and that the effects of tributyltin chloride are due to inhibition of the ATPase, and collapse of the transmembrane H+-gradient through OH−-anion exchange.

scholarly journals Steady-state kinetics of catecholamine transport by chromaffin-granule ‘ghosts’

1974 ◽  
Vol 144 (2) ◽  
pp. 319-325 ◽  
Author(s):  
J H Phillips
Keyword(s):  
Steady State ◽  
Competitive Inhibitor ◽  
Affinity Constant ◽  
Chromaffin Granule ◽  
Affinity Constants ◽  
Steady State Kinetics ◽  
Low Concentrations ◽  
High Concentrations ◽  
Chromaffin Granule Ghosts ◽  
Kinetics Of

Resealed chromaffin-granule ‘ghosts’ were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis–Menten kinetics, but affinity constants for the former substrates are in the range 8–18μm. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl2. Adenylyl (βγ-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29°C and does not seem to be identical with the Mg2+-stimulated adenosine triphosphatase of chromaffin granules.

scholarly journals VAMP2 AND SYNAPTOTAGMINS ARE RELATIVELY IMMOBILE ON CHROMAFFIN GRANULE MEMBRANES: IMPLICATIONS FOR MEMBRANE FUSION AND FUSION PORE EXPANSION

2021 ◽  
Author(s):  
Prabhodh S. Abbineni ◽  
Joseph S. Briguglio ◽  
Edwin R. Chapman ◽  
Ronald W. Holz ◽  
Daniel Axelrod
Keyword(s):  
Plasma Membrane ◽  
Membrane Fusion ◽  
Optical Resolution ◽  
Fusion Pore ◽  
Chromaffin Granule ◽  
Limited Mobility ◽  
Diffusion Characteristics ◽  
Granule Membrane ◽  
Fusion Site ◽  
Time Required

AbstractAlthough many of the proteins of secretory granules have been identified, little is known about their molecular organization and diffusion characteristics. Granule-plasma membrane fusion can only occur when proteins that enable fusion are present at the granule-plasma membrane contact. Thus, the mobility of granule membrane proteins may be an important determinant of fusion pore formation and expansion. To address this issue, we measured the mobility of (fluorophore-tagged) vesicle associated membrane protein 2 (VAMP2), synaptotagmin 1 (Syt1), and synaptotagmin 7 (Syt7) in chromaffin granule membranes in living chromaffin cells. We used a method that is not limited by standard optical resolution. A bright flash of strongly decaying evanescent field (∼80 nm exponential decay constant) produced by total internal reflection (TIR) was used to photobleach GFP-labeled proteins in the granule membrane. Fluorescence recovery occurs as unbleached protein in the granule membrane distal from the glass interface diffuses into the more bleached proximal regions, thereby enabling the measurement of diffusion coefficients. The studies revealed that VAMP2, Syt1, and Syt7 are relatively immobile in chromaffin granules membranes with diffusion constants of ≤ 3 × 10−10 cm2/s. Utilizing these diffusion parameters and the known density of VAMP2 and Syt 1 on synaptic vesicles, we estimated the time required for these proteins to arrive at a nascent fusion site to be tens of milliseconds. We propose that the mobilities of secretory granule SNARE and Syt proteins, heretofore unappreciated factors, influence the kinetics of exocytosis and protein discharge.Significance StatementIn eukaryotic cells, secretory vesicles fuse with the plasma membrane to secrete chemical transmitters, hormones and proteins that enable diverse physiological functions including neurotransmission. Fusion proteins need to be assembled at the fusion site in sufficient number in order to enable membrane fusion. However, the diffusion characteristics of fusogenic proteins on secretory vesicles remained unknown. Here we used a novel method not limited by standard optical resolution to measure the diffusion of VAMP2 and synaptotagmins on chromaffin granule membranes. We found they have limited mobility. The time required for these proteins to reach the granule-plasma membrane contact site suggests that their limited mobility likely influences the kinetics of membrane fusion and subsequent fusion pore expansion.

scholarly journals Stoichiometry of catecholamine/proton exchange across the chromaffin-granule membrane

1980 ◽  
Vol 192 (1) ◽  
pp. 273-278 ◽  
Author(s):  
J H Phillips ◽  
D K Apps
Keyword(s):  
Transport Model ◽  
Proton Exchange ◽  
Ph Gradient ◽  
Chromaffin Granule ◽  
Amine Concentration ◽  
Low Concentrations ◽  
Granule Membrane ◽  
Chromaffin Granule Ghosts

Catecholamines are accumulated by bovine chromaffin-granule “ghosts” in the presence of MgATP at 25 degrees C. With low concentrations of catecholamine, ratios of internal to external amine concentration of up to 20 000 were obtained. These values fit well with a transport model in which amine accumulation is both electrogenic and dependent on a pH gradient across the membrane.

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