Ca++-induced fusion of proteoliposomes: Dependence on transmembrane osmotic gradient

Miller, Christopher S.; Arvan, Peter; Telford, John N.; Racker, Efraim

doi:10.1007/bf01869672

Cited by 117 publications

(33 citation statements)

References 16 publications

(15 reference statements)

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“…If Ca2+ and Mg 2 + are added to the liposomes simultaneously, the effect of both ions is additive (Table II). These characteristics are very similar to properties found with divalent cation-induced liposome fusion in other model systems [37][38][39][40][41][42][43][44].…”

Section: Fusion 01 Liposomessupporting

confidence: 83%

“…7). The later observation is in contrast to so me other investigations, where complete cessation of liposome fusion was observed [41,44]. An explanation for the time couse observed in this study would be that fusion capacity is inversely re la ted to the diameter of liposomes.…”

Section: Time Course and Ca 2 + Gradientcontrasting

confidence: 78%

“…2 and 7). This is faster than the time course for the fusion of other types of liposomes reported so far [37,39,43,44]. Therefore the fast time course of secretion can be very weil compatible with a membrane fusion event.…”

Section: Time Course and Ca 2 + Gradientmentioning

confidence: 60%

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Membrane fusion of secretory vesicles and liposomes Two different types of fusion

Ekerdt

Dahl²,

Gratzl³

1981

Biochimica et Biophysica Acta (BBA) - Biomembranes

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Secretory vesieles isolated from adrenal medulla were found to fuse in vitro in response to incubation with Ca 2 +. Intervesicular fusion was detected by electron microscopy and was indicated by the appearance of twinned vesieies in freeze-fractured suspensions of vesieles and in thin-sectioned pellet. Two types of fusion could be distinguished: Type I, occurring between 10-7 M and 10-4 M Ca 2 +, was specific for ea 2 +, was inhibited by other divalent cations and was abolished by pretreatment of vesieles with glutaraldehyde, neuraminidase or trypsin. Fusion type I was linear with temperature. A second type of intervesicular fusion was elicited by Ca 2 + in concentrations higher than 2.5 mM and was morphologically characterized by multiple fusions of secretory vesicles. This type of fusion was found to be similar to fusion of liposomes prepared from the membrane lipids of adrenal medullary secretory vesieles: ea 2 + could be replaced by other divalent cations, the effect of different divalent cations was additive and pretreatments attacking membrane proteins were ineffective. Fusion type 11 of intact secretory vesieies as weil as liposome fusion was discontinuous with temperature. Liposome fusion could be detected within 35 ms and persisted for 180 min. Using liposomes containing defined Ca 2 + concentrations we have not found a major influence of Ca 2 + asymmetry on fusion. Incorporation of the ganglioside GM 3 , which is present in the membranes of intact adrenal medullary secretory vesicles did not change the properties of liposomes fusion. Using a Ca 2 +-selective electrode we have identified in secretory vesiele membranes both high affinity binding sites for Ca 2 + (/(} = 1.6 . 10-6 M) and low affinity sites (/(} = 1.2· 10-4 M).

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Section: Fusion 01 Liposomessupporting

confidence: 83%

Section: Time Course and Ca 2 + Gradientcontrasting

confidence: 78%

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Membrane fusion of secretory vesicles and liposomes Two different types of fusion

Ekerdt

Dahl²,

Gratzl³

1981

Biochimica et Biophysica Acta (BBA) - Biomembranes

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“…By using this technique, we could determine whether fusion of bilayer-attached liposomes was completely due to their osmotically induced swelling achieved by the addition of the osmoticum to the cis -compartment of the bilayer. By using membrane impermeable solutes, the presence of an open channel permeable for the osmotically active solute is essential (Miller et al, 1976;Woodbury and Miller, 1990; for details, see Methods). Because the OEP24 channel has its highest open probability at V m ϭ 0 mV, this method is suited ideally for testing permeation of substances through the open pore.…”

Section: Resultsmentioning

confidence: 99%

“…Neither ion was able to promote fusion on its own. All other conditions were as outlined previously (Miller et al, 1976;Woodbury and Miller, 1990).…”

Section: Electrophysiologically Monitored Osmotic Permeation Assaymentioning

confidence: 99%

A High-Conductance Solute Channel in the Chloroplastic Outer Envelope from Pea

et al. 1998

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The pea chloroplastic outer envelope protein OEP24 can function as a general solute channel. OEP24 is present in chloroplasts, etioplasts, and non-green root plastids. The heterologously expressed protein forms a voltage-dependent, high-conductance ( ⌳ ‫؍‬ 1.3 nS in 1 M KCl), and slightly cation-selective ion channel in reconstituted proteoliposomes. The highest open probability ( P open Ϸ 0.8) is at 0 mV, which is consistent with the absence of a transmembrane potential across the chloroplastic outer envelope. The OEP24 channels allow the flux of triosephosphate, dicarboxylic acids, positively or negatively charged amino acids, sugars, ATP, and Pi. Structure prediction algorithms and circular dichroism spectra indicate that OEP24 contains seven amphiphilic ␤ strands. The primary structure of OEP24 shows no homologies to mitochondrial or bacterial porins on a primary sequence basis, and OEP24 is functionally not inhibited by cadaverine, which is a potent inhibitor of bacterial porins. We conclude that OEP24 represents a new type of solute channel in the plastidic outer envelope. INTRODUCTIONCarbon dioxide reduction and its assimilation into carbohydrates, amino acids, fatty acids, and terpenoid compounds (Douce and Joyard, 1990) take place in chloroplasts. Annually, ‫ف‬ 120 ϫ 10 9 tons of CO 2 is converted into organic substances by chloroplasts of higher land plants. In addition, chloroplasts are the sole site of nitrite and sulfate reduction (Anderson, 1990;Crawford, 1995) and their assimilation in organic compounds. Chloroplasts are surrounded by a pair of double membranes, the inner and the outer envelopes, which delimit spatially and temporally the chloroplastic compartment from the cytoplasm. Both outer and inner envelope membranes differ in structure, function, and biochemical properties but also cooperate, for example, in the synthesis of lipids or in protein translocation. The various biosynthetic functions of the chloroplasts require the existence of different and effective transport mechanisms of solutes across the envelope membranes to provide the cell with carbohydrates, organic nitrogen, and sulfur compounds. On the other hand, chloroplasts take up inorganic cations (K ϩ , Na ϩ , Mg 2 ϩ , and Ca 2 ϩ ), anions (nitrite, sulfate, and phosphate), and a variety of organic biosynthetic pathway intermediates, such as phosphoenolpyruvate, dicarboxylic acids, acetate, amino acids, and ATP to fulfill their biosynthetic tasks.The outer envelope membrane is assumed to be freely permeable for most small molecular weight solutes (Flügge and Benz, 1984), like the outer membranes of mitochondria and Gram-negative bacteria (reviewed in Benz, 1994;Nikaido, 1994). The permeability of the outer membranes of mitochondria and Gram-negative bacteria is caused by poreforming proteins, designated porins, which share structural and functional features. Similar to these systems, the osmotic barrier against the cytosol is formed by the inner envelope membrane, containing specific carrier proteins of which some have been iden...

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Ultrastructural changes during stimulation of amphibian oxyntic cells viewed by scanning and transmission electron microscopy

Logsdon

Machen

1982

Anat. Rec.

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Amphibian oxyntic cells exposed by cryofracture were examined by field emission scanning electron microscopy. Comparisons were made between the structure thus revealed and those seen in thin-sectioned material from the same mucosas examined by transmission electron microscopy. Resting oxyntic cells had apical surfaces which were relatively smooth with some short microvilli. Apical cytoplasm was filled with smooth membrane tubules (so-called vesicotubules). Stimulation with a combination of histamine, dibutyryl cyclic AMP, and isobutylmethylxanthine (a phosphodiesterase inhibitor) led to a dramatic elaboration (i.e., increased membrane surface area) and a decrease in number of vesicotubules in the apical cytoplasm. The surface morphology of the stimulated oxyntic cell was much different from that reported for the mammalian parietal cell. Two types of surface elaboration were observed. Most commonly the surface was formed of flattened microplicae or lingulae. An irregular surface formed by the swelling of enlarged spaces near the apical surface was also observed. These new data have been used to evaluate the models which have been proposed to explain the nature of the transition from resting to stimulated morphology. A new model, which incorporates fusion of intracellular vesicotubules with each other and also with apical membrane, is proposed. The proposed fusion process may cause an increase in membrane area open to the extracellular (luminal)solution within the cell (rather than the eversion of membranes into the gastric lumen). Expansion of spaces between the microplicae may be caused by hydroosmotic pressures developed during active HCI secretion.

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Ca++-induced fusion of proteoliposomes: Dependence on transmembrane osmotic gradient

Cited by 117 publications

References 16 publications

Membrane fusion of secretory vesicles and liposomes Two different types of fusion

Membrane fusion of secretory vesicles and liposomes Two different types of fusion

A High-Conductance Solute Channel in the Chloroplastic Outer Envelope from Pea

Ultrastructural changes during stimulation of amphibian oxyntic cells viewed by scanning and transmission electron microscopy

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