Cold‐induced release of hormones and proteins from nerve endings isolated from bovine neural lobes

Biochimica et Biophysica Acta (BBA) - Biomembranes

Russel

et al. 1977

(In suspensions containing secretory vesicles as well as sheets of cell membrane, release of vasopressin parallel to intervesicular fusion and fusion of secretory vesicles with sheets of cell membrane was observed after exposure to Ca 2+ . Mg 2+ and Sr 2+ were ineffective in replacing Ca 2+ as trigger for fusion or vasopressin release.Intervesicular fusion and exocytotic profiles were observed when isolated neurohypophyses or neurosecretosomes were exposed to cold. IntroductionIt is well established that the passage of.Ca 2+ across the cell membrane is a critical step in stimulus-secretion coupling in the neurohypophysis [1,2,3]. Although Ca 2+ influx is apparently too small to be reliably quantitated [4], experiments with Ca 2+ transport inhibitors [2] bear out this contention. Also, treatment of isolated neurohypophyses with ionophores, which increase intracellular, free Ca 2+ concentration by increasing transmembrane transport, can induce secretion [5,6]. Both ultrastructural [7] and biochemical [8,9] studies suggest that secretion in the neurohypophysis as in various other endocrine systems [10], occurs by exocytosis. However, the events that are triggered by

Section: Exocytosis In Cold-stimulated Isolated Neurohypophyses and Nmentioning

confidence: 59%

Section: Exocytosis In Cold-stimulated Isolated Neurohypophyses and Nmentioning

confidence: 83%

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Fusion of neurohypophyseal membranes in vitro

Gratzil

Biochimica et Biophysica Acta (BBA) - Biomembranes

Russel

et al. 1977

“…The fusion of secretory vesicles isolated from rat liver displayed no abrupt changes between 2 and 37 ~ The detection of membrane fusion of biological membranes in vitro at low temperatures is not surprising: Exposed to cold, neurohypophyses [21], synaptosomes [62], and neurosecretosomes [4] release secretory products in the absence or presence of an external stimulus.…”

Section: Ca2+-speco~'icity Antagonism With Mg 2+ and Temperature Depmentioning

confidence: 96%

“…In contrast, chemically induced fusion of cells was shown to be enhanced by lysolecithin [14,43,60]. 4 Studies with phospholipid membranes have not clarified the effect of lysolecithin on fusion [10,56]. The results obtained so far indicate that membrane fusion occurring naturally during muscle development or secretion is inhibited by lysolecithin.…”

Section: Effect Of Various Substances On Ca 2 +-Induced Fusionmentioning

confidence: 99%

Fusion of secretory vesicles isolated from rat liver

Gratzl

1978

J. Membrain Biol.

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

Cold-induced insulin release in vitro: Evidence for exocytosis

Henquin

1978

Cell Tissue Res.

Exposure of isolated pancreatic islets (mouse or rat) to low temperature (2 degrees C) evoked a threefold increase in insulin release irrespective of the glucose concentration in the incobation medium. Cold-induced release was transient and rewarming to 37 degrees C restored the sensitivity of B-cells to gluocose stimulation. In islets cooled to 2 degrees C, exocytotic profiles could easily be detected both by thin-section and freeze-fracture electron microscopy. As revealed by the freeze-fracture technique, the number of exocytotic profiles per membrane area was increased three- to fourfold as compared to islet cells incubated at 20 degrees C. This was paralleled by intracellular fusion of secretory vesicles. Cold-induced insulin release was not affected by theophylline, cytochalasin B, omission of extracellular Ca++ or D600. Replacement of extracellular Na+ with choline or sucrose suppressed the increase in insulin release and in frequency of exocytotic profiles recorded after exposure to 2 degrees C. It is suggested that a redistribution of Ca++ from intracellular stores, possibly mediated by an increase in intracellular Na+ triggers exocytosis of insulin granules upon exposure to cold.