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101.
Per-Olof Berggren Birgitta Andersson Bo Hellman 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,720(3):320-328
Electrothermal atomic absorption spectroscopy was employed for measuring barium in β-cell-rich pancreatic islets microdissected from ob/ob-mice. Both the uptake and efflux of barium displayed two distinct phases. There was a 4-fold accumulation of barium into intracellular stores when its extracellular concentration was 0.26 mM. Unlike divalent cations with more extensive intracellular accumulation, the washout of Ba2+ was not inhibited by d-glucose. Ba2+ served as a substitute for Ca2+ both in maintaining the glucose metabolism after removal of extracellular Ca2+ and making it possible for glucose to stimulate insulin release. Furthermore, Ba2+ elicited insulin release in the absence of glucose and other secretagogues. The latter effect was reversible and was markedly potentiated under conditions known to increase the β-cell content of cyclic AMP. It is likely that the observed actions of Ba2+ are mediated by Ca2+, since Ca2+-dependent regulatory proteins, such as calmodulin, apparently cannot bind Ba2+ specifically. 相似文献
102.
N. B. M. Brantjes 《Plant Systematics and Evolution》1982,141(1):41-52
Polygala vauthieri andP. monticola var.brizoides have secondary pollen presentation from a basket-like structure on the style apex. This basket is loaded after the first visit by a bee. Pollen reception, therefore, can precede the issue of pollen. A sticky stigma secretion glues the pollen from the basket under the head of the bee visitor in an exactly predetermined spot on the left side only. This position mostly forms a kind of safe spot, where the bee can not remove the pollen. The exact position on the bee's head is determined by the species specific distance between style tip and nectary in the visited flower. In this way the two sympatric species deposit the pollen 2 mm apart on the visitor and so can avoid hybridization pollination, while being visited by the same group of bees. 相似文献
103.
Further characterization of the aggregation and fusion of chromaffin granules by synexin as a model for compound exocytosis 总被引:1,自引:0,他引:1
Synexin was isolated from bovine liver and found to aggregate adrenal chromaffin granules in the same Ca2+-dependent manner as previously described for adrenal synexin. The chromaffin granule aggregating activity of liver synexin was blocked in vitro by the addition of an antibody prepared to the 47,000 molecular weight band extracted from an SDS gel of an adrenal medullary synexin preparation. Chromaffin granules aggregated by synexin fused when exposed to cis-unsaturated fatty acids at concentrations comparable to those released from phospholipids by stimulated secretory cells. The synexin-induced aggregation reaction was blocked by Erythrosin B, a common food coloring, and by the phenothiazine antipsychotic trifluoperazine and promethazine. The aggregation and fusion of chromaffin granules thus appears to be a useful model system for studying synexin from diverse tissues and for testing pharmacologically or toxicologically active substances for effects on secretory systems. 相似文献
104.
The bioelectric responses at fertilization of the sea urchin Lytechinus variegatus are a complex series of membrane potential and resistance changes that occur concomitant with gamete fusion, ionic fluxes, and the cortical granule discharge. This work attempts to separate the electrical effects of sperm-egg interactions from those of the cortical reactions. Two approaches were taken to discern the electrical events associated with insemination, distinct from cortical granule discharge: (1) fertilization of eggs treated with 3% urethane, 10 mM procaine, or 10 mM nicotine, to prevent the cortical reaction and (2) refertilization of fertilized eggs (denuded with 1 mM aminotriazole containing 1 mg/ml soybean trypsin inhibitor). Cortical granule discharge in the absence of sperm incorporation was investigated by artificial activation with 5 μM A23187 or by fertilization in the presence of 10 μM cytochalasin D, which prevents incorporation. These results are consistent with a model in which the sperm-egg interaction triggers both a rapid (50–400 msec), but minor (?10 mV), electrical transient that leads to an action potential and then both the Na+-dependent fast block to polyspermy and the late block resulting from the secretion of the cortical granules. 相似文献
105.
In vivo increase in haemolymph volume of canavanine-treated locusts substantiates our previous in vitro findings that canavanine inhibits fluid secretion by locust Malpighian tubules. Furthermore when diuretic hormone is applied in vivo after canavanine treatment haemolymph volume is drastically reduced below levels retained in locusts untreated with canavanine. Again this is in accord with canavanine potentiation of semi-isolated Malpighian tubules and enhanced fluid secretion in vitro. The response is specific to canavanine; compounds similar in structure (arginine, argininic acid, citrulline, canaline, ornithine and homoserine) have no effect on the rate of fluid secreted by Malpighian tubules. Only partial competition is obtained with uridine homoserine. 相似文献
106.
Allan S. Schneider Hollis T. Cline Kurt Rosenheck † Martin Sonenberg 《Journal of neurochemistry》1982,37(3):567-575
Abstract: The catecholamine secretory function of a preparation of isolated bovine adrenal chromaffin cells has been further characterized under conditions designed to elucidate the mechanism of calcium channel activation and the possible role of cytoskeletal elements in stimulus-secretion coupling. Three related sets of data were obtained: (1) Differences in kinetics, Ca dependence, strength, and additivity of the secretory response to acetylcholine (ACh) versus excess K; (2) the effects on secretion of the Ca channel-blocking agents, Ni, Mg, and verapamil; and (3) the Ca dependence of vinblastine action on ACh- and K-evoked secretion. The results suggest that a major portion of the Ca influx required for catecholamine release enters the cell via voltage-dependent Ca channels with some additional Ca influx via the ACh receptor channel. Comparison of the present secretion data with corresponding known electrophysiological properties of isolated chromaffin cells provides added evidence for a role of chromaffin cell action potentials in regulation of Ca influx and the secretory response. Elevated Ca concentrations enhanced K-evoked secretion to levels comparable to that of ACh but did not induce a vinblastine block of K-evoked release. This provides further evidence against a role of microtubules in the common exocytosis event per se. However, a role of cytoskeletal elements in directing the movement of secretory granules, or an action of vinblastine at cholinergic receptors, remain distinct possibilities. 相似文献
107.
By placing seedlings of sunflower (Helianthus annuus L.) or maize (Zea mays L.) on agar plates containing a pH indicator dye it is possible to observe surface pH patterns along the growing seedling by observing color changes of the indicator dye. Using this method we find that in geotropically stimulated sunflower hypocotyls or maize coleoptiles there is enhanced proton efflux on the lower surface of the organ prior to the initiation of curvature. As curvature develops the pattern of differential acid efflux becomes more intense. A similar phenomenon is observed when these organs are exposed to unilateral illumination, i.e. enhanced acid efflux occurs on the dark side of the organ prior to the initiation of phototropic curvature and the pattern of differential acid efflux intensifies as phototropic curvature develops. These observations indicate that differential acid efflux occurs in response to tropistic stimuli and that the acid efflux pattern may mediate the development of tropistic curvatures. 相似文献
108.
Pancreatic polypeptide (PP) cells were studied in human endocrine pancreatic tumours and in normal human pancreata by immunohistochemical techniques and electron miscroscopy. The existence of long cytoplasmic processes was demonstrated both in tumours and normal tissue. These processes are in close contact with other endocrine cells or with acinar cells. This particular morphological aspect suggests that PP cells may control the function of other cells via paracrine secretion. 相似文献
109.
Julien Deschênes Jean-Paul Valet Normand Marceau 《In vitro cellular & developmental biology. Plant》1980,16(8):722-729
Summary The two-step collagenase perfusion method originally developed for the high yield isolation of parenchymal cells from adult
rat livers has been adapted to rats of 1 day, 1 week, and 3 weeks of age. The use of this method to isolate hepatocytes from
five or six rats of the respective ages demonstrated its reliability in terms of cell yield, percentage of single cells, and
cell viability. In all cases, hepatocytes attach with high efficiency to fibronectin precoated dishes using serum-free culture
medium. The dynamics of spreading is faster for newborn hepatocytes than adult ones. The functional integrity of these parenchymal
liver cells was assessed by their capacity to secrete albumin and α-fetoprotein in serum-free medium and to express lactate
dehydrogenase activity over a 24-hr period in primary culture.
Part of this work was presented at the 30th Annual Meeting of the Tissue Culture Association, Seattle, June, 1979. 相似文献
110.
The relationship between cellular dispersion and steroidogenesis was studied in culture using oocyte-cumulus complexes harvested from porcine follicles. The cells were cultured in modified TC 199 containing pig serum for one to two days. When oocyte-cumulus complexes were cultured in the absence of hormone the oocytes resumed meiosis, the cumulus cells grew out forming monolayers, and progesterone accumulation was low. Addition of ovine LH, purified human LH, or purified human FSH stimulated expansion of the cumulus mass as well as enhanced progesterone accumulation. Oocyte maturation was not affected by the hormones. In absence of hormone, oocyte-cumulus complexes obtained from large (6–12 mm) follicles showed increased cellular dispersion and higher progesterone accumulation as compared to complexes obtained from medium-sized (3–5 mm) follicles. 相似文献