Spontaneous and action potential-evoked Ca2+ release from endoplasmic reticulum in neocortical synaptic boutons

1. During presynaptic inhibition, an increased conductance in the membrane of the presynaptic bouton is presumed to reduce the action potential, thereby reducing transmitter release. The object of the simulation has been to determine the magnitude of a chloride conductance required to reduce transmitter release, for various diameters of synaptic boutons, connected to axons with diameters in the range 0.1-1.0 microns. 2. A propagating action potential was simulated in axons connected to either side of a hemispherical bouton. The axons could be myelinated or unmyelinated, while the bouton membrane could be passive, a node of the myelinated nerve, or have the same active properties as the attached unmyelinated nerve. Membrane properties of the axons were derived from mammalian data and scaled to 37 degrees C. 3. A steady-state chloride conductance was included in the bouton membrane, with ECl = -40 mV. The amplitude of the action potential in the bouton was calculated for different diameters of axon and bouton and for different magnitudes of chloride conductance. 4. Using published data on the relationship between the amplitude of a presynaptic action potential and the resulting postsynaptic potential, the relationship between the chloride conductance and the postsynaptic response was calculated for different geometries. Transmitter release was reduced when an action potential was 90 mV or smaller, with no transmission for action potentials smaller than 50 mV. 5. Conductance increases in the range 3 to 10 nS were required to reduce the action potential to 90 mV, depending on the diameter of the axon (0.5-1.0 microns), diameter of the bouton (3-6 microns), whether the bouton had passive or active membrane, and whether the axon was myelinated or unmyelinated. A 3 microns passive bouton connected to a 0.5 micron myelinated axon was most sensitive to the effects of a chloride conductance, while a 6 microns active bouton connected to a 1 micron myelinated nerve was least sensitive to the effects of a chloride conductance. 6. The reduction in the action potential was compared when ECl = -40 mV and when ECl = E(rest) = -80 mV. Inactivation of the sodium conductance by terminal depolarization was the dominant influence on the amplitude of the action potential. 7. Conductances that were sufficient to completely block synaptic transmission at a bouton were insufficient to prevent the spread of the action potential away from that bouton.(ABSTRACT TRUNCATED AT 400 WORDS)

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Upregulation of Calcium Homeostatic Mechanisms in Chronically Depolarized Rat Myenteric Neurons

Journal of Neurophysiology ◽

10.1152/jn.1999.81.6.2683 ◽

1999 ◽

Vol 81 (6) ◽

pp. 2683-2695 ◽

Cited By ~ 4

Author(s):

David J. Fickbohm ◽

Alan L. Willard

Keyword(s):

Endoplasmic Reticulum ◽

Action Potential ◽

Voltage Clamp ◽

Action Potentials ◽

Ion Concentration ◽

Electrophysiological Recording ◽

Activity Levels ◽

Myenteric Neurons ◽

Neuronal Processes ◽

Homeostatic Mechanisms

Upregulation of calcium homeostatic mechanisms in chronically depolarized rat myenteric neurons. Perturbations of intracellular Ca2+ ion concentration ([Ca2+]i) have important effects on numerous neuronal processes and influence development and survival. Neuronal [Ca2+]i is, in large part, dependent on activity, and changes in activity levels can alter how neurons handle calcium (Ca). To investigate the ability of neuronal Ca homeostatic mechanisms to adapt to the persistent elevation of [Ca2+]i, we used optical and electrophysiological recording techniques to measure [Ca2+]i transients in neurons from the rat myenteric plexus that had been chronically depolarized by growth in culture medium containing elevated (25 mM) KCl. When studied in normal saline, neurons that had previously been chronically depolarized for 3–5 days had briefer action potentials than control neurons, their action potentials produced smaller, more rapidly decaying increases in [Ca2+]i, and voltage-clamp pulses with action potential waveforms evoked smaller Ca currents than in control neurons. Simultaneous voltage-clamp measurements and calcium imaging revealed that increases in the Ca handling capacities of the chronically depolarized neurons permitted them to limit the amplitudes of action potential-evoked [Ca2+]i transients and to restore [Ca2+]i to basal levels more rapidly than control neurons. Release of Ca from endoplasmic reticulum-based Ca stores made smaller contributions to action potential-evoked [Ca2+]i transients in chronically depolarized neurons even though those neurons had larger caffeine-releasable Ca stores. Endoplasmic reticulum-based Ca sequestration mechanisms appeared to contribute to the faster decay of [Ca2+]i transients in chronically depolarized neurons. These results demonstrate that when neurons experience prolonged perturbations of [Ca2+]i, they can adjust multiple components of their Ca homeostatic machinery. Appropriate utilization of this adaptive capability should help neurons resist potentially lethal metabolic and environmental insults.

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In Vitro Induction of Crystals of MT Protein by Vinblastine-Colcemid in Mouse Spermatids

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100050676 ◽

1974 ◽

Vol 32 ◽

pp. 132-133

Author(s):

John J. Wolosewick ◽

John H. D. Bryan

Keyword(s):

Endoplasmic Reticulum ◽

Smooth Endoplasmic Reticulum ◽

Nuclear Ring ◽

Rough Er ◽

Distal Direction ◽

In Vitro Induction

Early in spermiogenesis the manchette is rapidly assembled in a distal direction from the nuclear-ring-densities. The association of vesicles of smooth endoplasmic reticulum (SER) and the manchette microtubules (MTS) has been reported. In the mouse, osmophilic densities at the distal ends of the manchette are the organizing centers (MTOCS), and are associated with the SER. Rapid MT assembly and the lack of rough ER suggests that there is an existing pool of MT protein. Colcemid potentiates the reaction of vinblastine with tubulin and was used in this investigation to detect this protein.

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Ultrastructure of the Parotid Gland of the Nine-Banded Armadillo

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100080626 ◽

1977 ◽

Vol 35 ◽

pp. 640-641

Author(s):

J. R. Ruby

Keyword(s):

Endoplasmic Reticulum ◽

Parotid Gland ◽

Periodic Acid ◽

Acinar Cells ◽

Duct System ◽

Parotid Glands ◽

Dasypus Novemcinctus ◽

Anterior Portion ◽

Periodic Acid Schiff ◽

Thin Sections

Parotid glands were obtained from five adult (four male and one female) armadillos (Dasypus novemcinctus) which were perfusion-fixed. The glands were located in a position similar to that of most mammals. They extended interiorly to the anterior portion of the submandibular gland.In the light microscope, it was noted that the acini were relatively small and stained strongly positive with the periodic acid-Schiff (PAS) and alcian blue techniques, confirming the earlier results of Shackleford (1). Based on these qualities and other structural criteria, these cells have been classified as seromucous (2). The duct system was well developed. There were numerous intercalated ducts and intralobular striated ducts. The striated duct cells contained large amounts of PAS-positive substance.Thin sections revealed that the acinar cells were pyramidal in shape and contained a basally placed, slightly flattened nucleus (Fig. 1). The rough endoplasmic reticulum was also at the base of the cell.

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Organisation in the Structure of the Cytoplasmic Ground Substance

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100070357 ◽

1978 ◽

Vol 36 (3) ◽

pp. 627-639

Author(s):

K.R. Porter

Keyword(s):

Endoplasmic Reticulum ◽

Golgi Complex ◽

Random Distribution ◽

Ground Substance ◽

The Matrix ◽

Cell Processes ◽

Cytoplasmic Ground Substance

Most types of cells are known from their structure and overall form to possess a characteristic organization. In some instances this is evident in the non-random disposition of organelles and such system subunits as cisternae of the endoplasmic reticulum or the Golgi complex. In others it appears in the distribution and orientation of cytoplasmic fibrils. And in yet others the organization finds expression in the non-random distribution and orientation of microtubules, especially as found in highly anisometric cells and cell processes. The impression is unavoidable that in none of these cases is the organization achieved without the involvement of the cytoplasmic ground substance (CGS) or matrix. This impression is based on the fact that a matrix is present and that in all instances these formed structures, whether membranelimited or filamentous, are suspended in it. In some well-known instances, as in arrays of microtubules which make up axonemes and axostyles, the matrix resolves itself into bridges (and spokes) between the microtubules, bridges which are in some cases very regularly disposed and uniform in size (Mcintosh, 1973; Bloodgood and Miller, 1974; Warner and Satir, 1974).

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Ultrastructural Changes Associated with Alcoholic Hyalin in Hepatocytes and Biliary Epithelial Cells

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066929 ◽

1971 ◽

Vol 29 ◽

pp. 572-573

Author(s):

Odell T. Minick ◽

Hidejiro Yokoo ◽

Fawzia Batti

Keyword(s):

Endoplasmic Reticulum ◽

Epithelial Cells ◽

Liver Biopsy ◽

Alcoholic Hepatitis ◽

Ultrastructural Changes ◽

Main Mass ◽

Biliary Epithelial Cells ◽

Biopsy Specimens ◽

Alcoholic Hyalin

To learn more of the nature and origin of alcoholic hyalin (AH), 15 liver biopsy specimens from patients with alcoholic hepatitis were studied in detail.AH was found not only in hepatocytes but also in ductular cells (Figs. 1 and 2), although in the latter location only rarely. The bulk of AH consisted of a randomly oriented network of closely packed filaments measuring about 150 Å in width. Bundles of filaments smaller in diameter (40-90 Å) were observed along the periphery of the main mass (Fig. 1), often surrounding it in a rim-like fashion. Fine filaments were also found close to the nucleus in both hepatocytes and biliary epithelial cells, the latter even though characteristic AH was not present (Figs. 3 and 4). Dispersed among the larger filaments were glycogen, RNA particles and profiles of endoplasmic reticulum. Dilated cisternae of endoplasmic reticulum were often conspicuous around the periphery of the AH mass. A limiting membrane was not observed.

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Compound Symbiosis in Peridinium Balticum

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100072940 ◽

1973 ◽

Vol 31 ◽

pp. 500-501

Author(s):

R. N. Tomas

Keyword(s):

Endoplasmic Reticulum ◽

Nuclear Envelope ◽

The Other ◽

Exact Nature ◽

Symbiotic Relationship

Peridinium balticum appears to be unusual among the dinoflagellates in that it possesses two DNA-containing structures as determined by histochemical techniques. Ultrastructurally, the two dissimilar nuclei are contained within different protoplasts; one of the nuclei is characteristically dinophycean in nature, while the other is characteristically eucaryotic. The chloroplasts observed within P. balticum are intrinsic to an eucaryotic photosynthetic endosymbiont and not to the dinoflagellate. These organelles are surrounded by outpocketings of endoplasmic reticulum which are continuous with the eucaryotic nuclear envelope and are characterized by thylakoids composed of three apposed lamellae. Girdle lamellae and membranebounded interlamellar pyrenoids are also present. Only the plasmalemma of the endosymbiont segregates its protoplast from that of the dinophycean cytoplasm. The exact nature of this symbiotic relationship is at present not known.

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Golgi Apparatus and Melanogenesis: Ultrastructural Study of a Human Cellular Blue Nevus (Melanocytoma)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100072344 ◽

1973 ◽

Vol 31 ◽

pp. 380-381

Author(s):

S.R. Allegra

Keyword(s):

Endoplasmic Reticulum ◽

Golgi Apparatus ◽

Ultrastructural Study ◽

The Other ◽

Blue Nevus ◽

Normal Complement ◽

Golgi Vesicles ◽

Golgi System ◽

The Subject ◽

Cellular Blue Nevus

The respective roles of the ribo somes, endoplasmic reticulum, Golgi apparatus and perhaps nucleus in the synthesis and maturation of melanosomes is still the subject of some controversy. While the early melanosomes (premelanosomes) have been frequently demonstrated to originate as Golgi vesicles, it is undeniable that these structures can be formed in cells in which Golgi system is not found. This report was prompted by the findings in an essentially amelanotic human cellular blue nevus (melanocytoma) of two distinct lines of melanocytes one of which was devoid of any trace of Golgi apparatus while the other had normal complement of this organelle.

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Modification of Pineal Ultrastructure by Exogenous Hormones

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100060866 ◽

1967 ◽

Vol 25 ◽

pp. 170-171

Author(s):

R. A. Turner ◽

A. E. Rodin ◽

D. K. Roberts

Keyword(s):

Electron Microscopy ◽

Endoplasmic Reticulum ◽

Rough Endoplasmic Reticulum ◽

Estradiol Benzoate ◽

Female Rats ◽

List Type ◽

Type Number ◽

Pregnant Rats ◽

Gonadal Atrophy ◽

Pineal Ultrastructure

There have been many reports which establish a relationship between the pineal and sexual structures, including gonadal hypertrophy after pinealectomy, and gonadal atrophy after injection of pineal homogenates or of melatonin. In order to further delineate this relationship the pineals from 5 groups of female rats were studied by electron microscopy:ControlsPregnant ratsAfter 4 weekly injections of 0.1 mg. estradiol benzoate.After 8 daily injections of 150 mcgm. melatonin (pineal hormone).After 8 daily injections of 3 mg. serotonin (melatonin precursor).No ultrastructural differences were evident between the control, and the pregnancy and melatonin groups. However, the estradiol injected animals exhibited a marked increase in the amount and size of rough endoplasmic reticulum within the pineal cells.

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Hepatic Ultrastructure Changes Induced by Lithocholic Acid

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100060829 ◽

1967 ◽

Vol 25 ◽

pp. 162-163 ◽

Cited By ~ 1

Author(s):

F. G. Zaki

Keyword(s):

Endoplasmic Reticulum ◽

Lithocholic Acid ◽

Smooth Endoplasmic Reticulum ◽

Protein Diet ◽

Low Protein Diet ◽

Electron Microscopic ◽

Hydropic Degeneration ◽

Hepatic Cells ◽

Low Protein ◽

Microscopic Studies

Addition of lithocholic acid (LCA), a naturally occurring bile acid in mammals, to a low protein diet fed to rats induced marked inflammatory reaction in the hepatic cells followed by hydropic degeneration and ductular cell proliferation. These changes were accompanied by dilatation and hyperplasia of the common bile duct and formation of “gallstones”. All these changes were reversible when LCA was withdrawn from the low protein diet except for the hardened gallstones which persisted.Electron microscopic studies revealed marked alterations in the hepatic cells. Early changes included disorganization, fragmentation of the rough endoplasmic reticulum and detachment of its ribosomes. Free ribosomes, either singly or arranged in small clusters were frequently seen in most of the hepatic cells. Vesiculation of the smooth endoplasmic reticulum was often encountered as early as one week after the administration of LCA (Fig. 1).

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