The Fine Structure Of Photoreceptors In Mitopus Morio (Phalangida)

1969 ◽  
Vol 4 (2) ◽  
pp. 327-351
Author(s):  
D. J. CURTIS
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membranes ◽  
Acetylcholinesterase Activity ◽  
Structural Studies ◽  
Hexagonal Array ◽  
Laminated Structure ◽  
Dense Bodies ◽  
Single Lens ◽  
Dioptric Apparatus ◽  
Stimulation Of

Fine structural studies on the eyes of the harvestman Mitopus morio revealed the presence of microvilli in the rhabdom. The microvilli vary in length between 1 µ and 2 µ, are about 800 Å wide, and curved or straight. They derive from the plasma membranes of the four retinula cells which surround the rhabdom. Approximately cylindrical in shape, the rhabdoms are about 40 µ long by about 4-6 µ in cross-diameter. Each rhabdom is situated at the centre of a retinula, and these retinulae are packed in a hexagonal array to form the retina. Distally, rhabdom fusion occurs to form a rhabdom network. The retina lies beneath the dioptric apparatus which consists of a single lens, surmounting a glassy body composed of lentigen cells. The cytoplasmic organelles of the retinula cells include mitochondria, lysosomes, sparse elements of endoplasmic reticulum, vesicular components, prominent Golgi complexes and pigment granules which possess a laminated structure. An important feature of the retinula cell is the presence of many small vesicles, about 0.1 µ in diameter, clustered beneath the rhabdom. Incubation of glutaraldehyde-fixed eyes in a Gomori medium with acetylthiocholine as substrate, coupled with inhibition of controls by 62C47, indicates the presence of a presumed acetylcholinesterase in these vesicles. Similar vesicles also occur in the proximal cytoplasm of the retinula cells. Other larger vesicles, often with a core of whorled membranes, as well as dense bodies, also show acetylthiocholine-splitting activity. This latter activity is not inhibited by 62C47 and is probably the effect of lysosomal non-specific esterase. These bodies also exhibit acid phosphatase activity when incubated in a Gomori medium with β-glycerophosphate as substrate. The presence of acetylcholinesterase activity, as distinct from non-specific esterase, in vesicles closely associated with the rhabdom and in more proximally situated vesicles is significant. It would point to the presence of an acetylcholine/acetylcholinesterase system involved in the generation and/or propagation of the sensory impulse arising from photo-stimulation of the rhabdom.

scholarly journals Inositol 1,4,5-trisphosphate mobilizes intracellular Ca2+ from permeabilized insulin-secreting cells

1984 ◽  
Vol 223 (2) ◽  
pp. 467-473 ◽  
Author(s):  
T J Biden ◽  
M Prentki ◽  
R F Irvine ◽  
M J Berridge ◽  
C B Wollheim
Keyword(s):  
Endoplasmic Reticulum ◽  
Steady State ◽  
Plasma Membranes ◽  
Cell Protein ◽  
Mitochondrial Activity ◽  
Rinm5f Cells ◽  
Cation Composition ◽  
Inositol 1,4,5 Trisphosphate ◽  
Insulin Secreting Cells ◽  
Stimulation Of

A possible role in secretory processes is proposed for inositol 1,4,5-triphosphate (IP3), based upon investigations of the Ca2+ steady state maintained by ‘leaky’, insulin-secreting RINm5F cells. These cells had been treated with digitonin to permeabilize their plasma membranes and thereby ensure that only intracellular Ca2+ buffering mechanisms were active. When placed in a medium with a cation composition resembling that of the cytosol, cells rapidly took up Ca2+ as measured by a Ca2+-specific minielectrode. Two Ca2+ steady states were observed. A lower level of around 120nM required ATP-dependent Ca2+ uptake and was probably determined by the endoplasmic reticulum. The higher steady state (approx. 800 nM), seen only in the absence of ATP, was shown to be due to mitochondrial activity. IP3 specifically released Ca2+ accumulated in the ATP-dependent pool, but not from mitochondria, since Ca2+ release was demonstrated in the presence of the respiratory poison antimycin. The IP3-induced Ca2+ release was rapid, with 50% of the response being seen within 15s. The apparent Km was 0.5 microM and maximal concentrations of IP3 (2.5 microM) produced a peak Ca2+ release of 10 nmol/mg of cell protein, which was followed by re-uptake. A full Ca2+ response was seen if sequential pulses of 2.5 microM-IP3 were added at 20 min intervals, although there was a slight (less than 20%) attenuation if the intervening period was decreased to 10 min. These observations could be related to the rate of IP3 degradation which, in this system, corresponded to a 25% loss of added 32P label within 2 min, and a 75% loss within 20 min. The results suggest that IP3 might act as a link between metabolic, cationic and secretory events during the stimulation of insulin release.

A possible structural basis for the extracellular release of acetylcholinesterase

1975 ◽  
Vol 191 (1103) ◽  
pp. 271-283 ◽  
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Envelope ◽  
Chromaffin Cells ◽  
Plasma Membranes ◽  
Cholinesterase Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Splanchnic Nerve ◽  
Ultrastructural Localization ◽  
Acetylcholinesterase Activity ◽  
Structural Basis

The ultrastructural localization of acetylcholinesterase and non-specific cholinesterase activity has been studied in sections of ox adrenal medulla by cytochemical methods. Non-specific cholinesterase activity, identified by using butyrylthiocholine as substrate and ethopropazine as inhibitor, occurs intracellularly in some adrenaline-containing chromaffin cells: the reaction end-product is deposited within the cisternae of the endoplasmic reticulum and in the nuclear envelope. Reaction end-product of non-specific cholinesterase also occurs in the endoplasmic reticulum of pericytes, around sinusoids and capillaries and within smooth muscle cells. Acetylcholinesterase activity, identified by using acetylthiocholine as substrate and BW 284C51 as inhibitor, occurs in both the splanchnic nerve and in chromaffin cells. Reaction end-product is found at the following sites (i) around myelinated and unmyelinated non-terminal axons of splanchnic nerve, between the axolemma and the Schwann cell membrane; (ii) within the cisternae of axonal smooth endoplasmic reticulum; sometimes these cisternae appear to be connected to the axolemma; (iii) between the axolemmas of preterminal axons and the plasma membranes of chromaffin cells; (iv) between the axolemmas of nerve terminals and the plasma membranes of chromaffin cells, including the synaptic cleft; (v) within cisternae of rough and smooth endoplasmic reticulum, and also within the nuclear envelope, of both adrenaline- and noradrenaline-containing chromaffin cells; (vi) between the plasma membranes of adjacent chromaffin cells, but only when one or both of these cells contain reaction product within the cisternae of its endoplasmic reticulum; these cisternae sometimes appear to be connected to the plasma membrane. These observations raise the question whether the acetylcholinesterase activity released from the perfused adrenal gland might originate from the cisternae of the endoplasmic reticula of splanchnic nerve and/or chromaffin cell.

scholarly journals STIMULATION OF GLUCOSE-6-PHOSPHATASE ACTIVITY IN THE MUCOSAL CELLS OF THE MOUSE INTESTINE

1973 ◽  
Vol 21 (5) ◽  
pp. 426-440 ◽  
Author(s):  
J. S. HUGON ◽  
D. MAESTRACCI ◽  
D. MÉNARD
Keyword(s):  
Endoplasmic Reticulum ◽  
Phosphatase Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Male Mice ◽  
Dense Bodies ◽  
Absorptive Cells ◽  
Mucosal Cells ◽  
Mouse Intestine ◽  
Stimulation Of

Adult Swiss ICR male mice were fed fructose or glucose for several days. Glucose-6-phosphatase activity in the duodenal and jejunal epithelium was measured by biochemical and cytophotometric means, and it was also localized cytochemically. The fructose diet stimulated glucose-6-phosphatase activity within 6 hr of feeding. The enzyme was stimulated more in the absorptive cells of the basal third than in those of the median and apical third of the villi. After 3 days of feeding of fructose, the smooth endoplasmic reticulum hypertrophied and occupied large areas in the absorptive cells. Lipoprotein spherules and polymorphic dense bodies were also observed. No such modifications were seen in glucose-fed animals.

scholarly journals CYTOLOGICAL ALTERATIONS RELATED TO STIMULATION OF THE ZONA GLOMERULOSA OF THE ADRENAL GLAND

1965 ◽  
Vol 26 (2) ◽  
pp. 499-521 ◽  
Author(s):  
Filiberto Giacomelli ◽  
Joseph Wiener ◽  
David Spiro
Keyword(s):  
Endoplasmic Reticulum ◽  
Adrenal Gland ◽  
Light And Electron Microscopy ◽  
Zona Glomerulosa ◽  
High Electron ◽  
Dense Bodies ◽  
Large Numbers ◽  
Cytological Alterations ◽  
Parallel Arrays ◽  
Stimulation Of

The structure of the zona glomerulosa of the rat adrenal gland stimulated by sodium restriction has been studied by light and electron microscopy. The major changes observed during the course of the experiment in stimulated glands involve cytoplasmic droplets, mitochondria, and the endoplasmic reticulum. There is a progressive decrease in the number of cytoplasmic droplets of low electron opacity. Numerous, greatly elongated mitochondria containing parallel arrays of tubules are noted. These tubules extend from within the mitochondria through gaps in the mitochondrial-limiting membranes into the cytoplasm. In addition, amorphous intramitochondrial deposits, possibly aldosterone precursors, are seen. Increased amounts of smooth-surfaced endoplasmic reticulum, often showing complex arrangements, are another feature of the stimulated zona glomerulosa. Other alterations include the presence of large numbers of dense bodies as well as cytoplasmic droplets of high electron opacity. These observations are discussed in relation to the biosynthesis of aldosterone.

Copper Localization in Cirrhotic Rat Liver by Scanning Electron Microscopy

1969 ◽  
Vol 27 ◽  
pp. 38-39 ◽  
Author(s):  
J. C. Russ ◽  
E. McNatt
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Electron Microscope ◽  
Copper Acetate ◽  
Lead Citrate ◽  
Dense Bodies ◽  
Transmission Electron ◽  
Electron Mode ◽  
Scanning Electron

In order to study the retention of copper in cirrhotic liver, rats were made cirrhotic by carbon tetrachloride inhalation twice weekly for three months and fed 0.2% copper acetate ad libidum in drinking water for one month. The liver tissue was fixed in osmium, sectioned approximately 2000 Å thick, and stained with lead citrate. The section was examined in a scanning electron microscope (JEOLCO JSM-2) in the transmission electron mode.Figure 1 shows a typical area that includes a red blood cell in a sinusoid, a disse, and a portion of the cytoplasm of a hepatocyte which contains several mitochondria, peribiliary dense bodies, glycogen granules, and endoplasmic reticulum.

scholarly journals Hepatic endosome fractions contain an ATP-driven proton pump

1985 ◽  
Vol 225 (1) ◽  
pp. 51-58 ◽  
Author(s):  
T Saermark ◽  
N Flint ◽  
W H Evans
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Atpase Activity ◽  
Proton Pump ◽  
Subcellular Distribution ◽  
Plasma Membranes ◽  
Specific Activity ◽  
Ph Gradients ◽  
Subcellular Organelle ◽  
Liver Homogenates

Endosome fractions were isolated from rat liver homogenates on the basis of the subcellular distribution of circulating ligands, e.g. 125I-asialotransferrin internalized by hepatocytes by a receptor-mediated process. The distribution of endocytosed 125I-asialotransferrin 1-2 min and 15 min after uptake by liver and a monensin-activated Mg2+-dependent ATPase activity coincided on linear gradients of sucrose and Nycodenz. The monensin-activated Mg2+-ATPase was enriched relative to the liver homogenates up to 60-fold in specific activity in the endosome fractions. Contamination of the endosome fractions by lysosomes, endoplasmic reticulum, mitochondria, plasma membranes and Golgi-apparatus components was low. By use of 9-aminoacridine, a probe for pH gradients, the endosome vesicles were shown to acidify on addition of ATP. Acidification was reversed by addition of monensin. The results indicate that endosome fractions contain an ATP-driven proton pump. The ionophore-activated Mg2+-ATPase in combination with the presence of undegraded ligands in the endosome fractions emerge as linked markers for this new subcellular organelle.

The biological activity of glucagon–phospholipid complexes

1983 ◽  
Vol 61 (7) ◽  
pp. 688-691 ◽  
Author(s):  
J. J. Liepnieks ◽  
P. Stoskopf ◽  
E. A. Carrey ◽  
C. Prosser ◽  
R. M. Epand
Keyword(s):  
Biological Activity ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Bovine Brain ◽  
Water Soluble ◽  
Dipalmitoyl Phosphatidylcholine ◽  
Dimyristoyl Phosphatidylcholine ◽  
Lipoprotein Complex ◽  
Stimulation Of

Glucagon can form water-soluble complexes with phospholipids. The incorporation of glucagon into these lipoprotein particles reduces the biological activity of the hormone. The effect is observed only at temperatures below the phase transition temperature of the phospholipid and results in a decreased stimulation of the adenylate cyclase of rat liver plasma membranes by the lipoprotein complex as compared with the hormone in free solution. Two- to five-fold higher concentrations of glucagon are required for half-maximal stimulation of adenylate cyclase when the hormone is complexed with dimyristoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine, or bovine brain sphingomyelin. A possible role of lipoprotein-associated hormones in the development of insulin resistance is discussed.

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