Ca<sup>2+</sup>‐induced fusion of golgi‐derived secretory vesicles isolated from rat liver

Gratzl, Manfred; Dahl, Gerhard

doi:10.1016/0014-5793(76)80038-5

Cited by 51 publications

(22 citation statements)

References 14 publications

(3 reference statements)

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“…Secretory vesicles isolated from the adrenal medulla, freeze-fractured in suspension after exposure to different Ca 2 + concentrations, have morphological characteristics similar to those found for various other types of secretory vesicles [13][14][15][16]: The vesieIes are dispersed in the medium when no Ca 2 + has been added, while vesicle-vesicle contacts and twinned vesicles (and a few triplets) are apparent in the presence of 10-4 M Ca 2 +. The continuous fracture plane in E and P-faces of twinned vesicles indicates that they are products of intervesicular fusion (for interpretation see also Ref.…”

Section: Fusion O[ Isolated Secretory Vesic/esmentioning

confidence: 92%

“…Further justification of this approach is given elsewhere [12]. In previous studies we have shown that secretory vesicles isolated from endocrine pancreas, neurohypophysis and liver can be induced to fuse by Ca 2 + [13][14][15][16]. We have concluded that a major role of Ca 2 + is the initiation of exocytotic membrane fusion by direct interaction with the membranes.…”

Section: Introductionmentioning

confidence: 99%

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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 O[ Isolated Secretory Vesic/esmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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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“…Fusion of isolated microsomal membranes, in contrast to Golgi-derived membranes, has not been observed [31]. Therefore, in the Golgi apparatus a reaction making vesicles "fusion competent" must occur.…”

Section: Effect Of Group-spec~c Reagents and Enzymesmentioning

confidence: 99%

“…Studies with intact cells have not yielded data which lead to ready interpretation concerning subcellular processes. On the other hand, studies with artificial membranes may be only tangentially related to the fusion of biological membranes.Recently our group investigated the fusion of isolated biological membranes [16,17,31,33,69,74]. We observed that Ca 2+ specifically induces the fusion of isolated secretory vesicles in a buffered sucrose medium.…”

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confidence: 99%

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Fusion of secretory vesicles isolated from rat liver

Gratzl

Dahl

1978

J. Membrain Biol.

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Summary. Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca 2 +. Vesicle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca 2 +-concentrations and is half maximal around 10 -6 M. Other divalent cations (Ba 2+, Sr 2+, and Mg 2+) were ineffective. Mg 2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesicles in vitro is Ca z+ specific and exhibits properties similar to the exocytotic process of various secretory cells.Various substances affecting secretion in vivo (microtubular inhibitors, local anesthetics, ionophores) were tested for their effect on membrane fusion in our system.The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca 2+, and in its Cag+-specificity. Chemical and enzymatic modifications of the vesicle membrane indicate that glycoproteins may account for these differences.Membrane fusion is an essential event in a variety of cell functions such as cell fusion, uptake of extracellular material (endocytosis) and release of cell products (exocytosis). Elucidation of the molecular mechanism of membrane fusion has been hampered by the lack of suitable systems for studying this process. Studies with intact cells have not yielded data which lead to ready interpretation concerning subcellular processes. On the other hand, studies with artificial membranes may be only tangentially related to the fusion of biological membranes.Recently our group investigated the fusion of isolated biological membranes [16,17,31,33,69,74]. We observed that Ca 2+ specifically induces the fusion of isolated secretory vesicles in a buffered sucrose medium.Intervesicular fusion of secretory vesicles, as well as the interaction between the cell membrane and the vesicle membrane, was observed in a variety of secretory cells [2,3,6,18,29,39,53,65]. Douglas [20] showed that in "compound exocytosis" by mast cells an external stimulus initiates fusion between secretory vesicle membranes and the

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