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1.
In this short review, we will first discuss localized cytoplasmic calcium signals in pancreatic acinar cells. In the second
part of the review, we will describe recently discovered polarized calcium efflux and calcium propagation through the lumen
of the endoplasmic reticulum — ER (a phenomenon we have termed “calcium tunnelling”). Finally, we will present a hypothesis
concerning the roles that these mechanisms could play in transcellular calcium flux. 相似文献
2.
We have developed a firing rate network model for working memory that combines Mexican-hat-like synaptic coupling with intrinsic
or cellular dynamics that are conditionally bistable. While our approach is in the spirit of Camperi and Wang (1998) we include
a specific and plausible mechanism for the cellular bistability. Modulatory neurotransmitters are known to activate second
messenger signaling systems, and our model includes an intracellular Ca2+ handling subsystem whose dynamics depend upon the level of the second messenger inositol 1,4,5 trisphosphate (IP3). This
Ca2+ subsystem endows individual units with conditional intrinsic bistability for a range of IP3. The full “hybrid” network sustains
IP3-dependent persistent (“bump”) activity in response to a brief transient stimulus. The bump response in our hybrid model,
like that of Camperi-Wang, is resistant to noise – its position does not drift with time.
Action Editor: Upinder Bhalla 相似文献
3.
Insect octopamine receptors: a new classification scheme based on studies of cloned Drosophila G-protein coupled receptors 总被引:1,自引:0,他引:1
Summary Insect octopamine receptors are G-protein coupled receptors. They can be coupled to second messenger pathways to mediate either increases or decreases in intracellular cyclic AMP levels or the generation of intracellular calcium signals. Insect octopamine receptors were originally classified on the basis of second messenger changes induced in a variety of intact tissue preparations. Such a classification system is problematic if more than one receptor subtype is present in the same tissue preparation. Recent progress on the cloning and characterization in heterologous cell systems of octopamine receptors from Drosophila and other insects is reviewed. A new classification system for insect octopamine receptors into “α-adrenergic-like octopamine receptors (OctαRs)”, “β-adrenergic-like octopamine receptors (OctβRs)” and “octopamine/tyramine (or tyraminergic) receptors” is proposed based on their similarities in structure and in signalling properties with vertebrate adrenergic receptors. In future studies on the molecular basis of octopamine signalling in individual tissues it will be essential to identify the relative expression levels of the different classes of octopamine receptor present. In addition, it will be essential to identify if co-expression of such receptors in the same cells results in the formation of oligomeric receptors with specific emergent pharmacological and signalling properties. 相似文献
4.
I. D. Nelson 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(2):147-155
In all four proboscis muscles of the whelk Buccinum undatum, the potassium-induced depolarization response was acutely dependent upon extracellular calcium, being eliminated in calcium-free
conditions. The responses to acetylcholine were found to be partly dependent upon intracellular calcium. Responses to the
peptides phenylalanine-methionine-arginine-phenylalanine-NH2 and phenylalanine-leucine-arginine-phenylalanine-NH2 were much more resistant to calcium-free conditions and appeared to engage the excitation-contraction coupling mechanism
by mobilizing stored intracellular calcium. Sucrose-gap studies of radular retractor muscles showed that the organic calcium
“antagonist” nifedipine enhanced potassium-induced depolarization responses, initiating spike-like action potentials and associated
fast twitch activity. The inorganic calcium antagonist gadolinium exerted concentration-dependent inhibitory actions on these
muscles. Basal tonus and fast twitch activity in response to potassium-induced depolarization were eliminated as were the
spike-like action potentials of the membrane electrical response. The inorganic calcium “antagonist” cadmium greatly enhanced
potassium-induced contractures in all four muscles, and on its own it induced tonic force and fast twitches in all the muscles.
It seems likely that cadmium may have displaced stored intracellular calcium to induce myofilament activation. While these
molluscan smooth muscles appear to possess calcium channels with fast and slow characteristics, their behaviour and pharmacological
manipulation is very different from their more well known mammalian transient and long-lasting channel counterparts. 相似文献
5.
P. G. Kostyuk 《Neurophysiology》1994,26(1):3-6
The paper summarizes recent data about the mechanisms that determine the kinetics and amplitude of transient elevations in the intracellular level of free calcium (calcium signals) in excitable cells. The relative role of various types of voltage-operated calcium channels, fast cytosolic buffering, active accumulation in intracellular stores, and extrusion of ions from the cell are discussed. New technical approaches enabling resolution of these questions are described.Neirofiziologiya/Neurophysiology, Vol. 26, No. 1, pp. 5–8, January–February, 1994. 相似文献
6.
Azzu V Yadin D Patel H Fraternali F Chantler PD Molloy JE 《European biophysics journal : EBJ》2006,35(4):302-312
Muscle myosins are molecular motors that convert the chemical free energy available from ATP hydrolysis into mechanical displacement
of actin filaments, bringing about muscle contraction. Myosin cross-bridges exert force on actin filaments during a cycle
of attached and detached states that are coupled to each round of ATP hydrolysis. Contraction and ATPase activity of the striated
adductor muscle of scallop is controlled by calcium ion binding to myosin. This mechanism of the so-called “thick filament
regulation” is quite different to vertebrate striated muscle which is switched on and off via “thin filament regulation” whereby
calcium ions bind to regulatory proteins associated with the actin filaments. We have used an optically based single molecule
technique to measure the angular disposition adopted by the two myosin heads whilst bound to actin in the presence and absence
of calcium ions. This has allowed us to directly observe the movement of individual myosin heads in aqueous solution at room
temperature in real time. We address the issue of how scallop striated muscle myosin might be regulated by calcium and have
interpreted our results in terms of the structures of smooth muscle myosin that also exhibit thick filament regulation.
This paper is not being submitted elsewhere and the authors have no competing financial interests 相似文献
7.
Stuart A. Newman 《Journal of biosciences》1992,17(3):193-215
Early embryos of metazoan species are subject to the same set of physical forces and interactions as any small parcels of
semi-solid material, living or nonliving. It is proposed that such “generic” properties of embryonic tissues have played a
major role in the evolution of biological form and pattern by providing an array of morphological templates, during the early
stages of metazoan phylogeny, upon which natural selection could act. The generic physical mechanisms considered include sedimentation,
diffusion, and reaction-diffusion coupling, all of which can give rise to chemical nonuniformities (including periodic patterns)
in eggs and small multicellular aggregates, and differential adhesion, which can lead to the formation of boundaries of non-mixing
between adjacent cell populations. Generic mechanisms that produce chemical patterns, acting in concern with the capacity
of cells to modulate their adhesivity (presumed to be a primitive, defining property of metazoa), could lead to multilayered
gastrulae of various types, segmental organization, and many of the other distinguishing characteristics of extant and extinct
metazoan body plans. Similar generic mechanisms, acting on small tissue primordia during and subsequent to the establishment
of the major body plans, could have given rise to the forms of organs, such as the vertebrate limbs. Generic physical processes
acting on a single system of cells and cell products can often produce a widely divergent set of morphological phenotypes,
and these are proposed to be the raw material of the evolution of form. The establishment of any ecologically successful form
by these mechanisms will be followed, under this hypothesis, by a period of genetic evolution, in which the recruitment of
gene products to produce the “generically templated” morphologies by redundant pathways would be favoured by intense selection,
leading to extensive genetic change with little impact on the fossil record. In this view, the stabilizing and reinforcing
functions of natural selection are more important than its ability to effect incremental change in morphology. Aspects of
evolution which are problematic from the standard neo-Darwinian viewpoint, or not considered within that framework, but which
follow in a straightforward fashion from the view presented here, include the beginnings of an understanding of why organisms
have the structure and appearance they’ do, why homoplasy (the recurrent evolution of certain forms) is so prevalent, why
evolution has the tempo and mode it does (“punctuated equilibrium”), and why a “rapid” burst of morphological evolution occurred
so soon after the origin of the metazoa. 相似文献
8.
Gametes of the unicellular green alga Chlamydomonas reinhardii recognize and adhere to cells of the opposite mating type by flagellar contact. Adhesion between these specialized organelles signals a rapid series of mating events which result in gamete fusion. The sequence of morphological changes (flagellar tip activation, cell wall loss, and mating structure elongation), which occur as a consequence of the sexual signalling, have been characterized. The signalling mechanisms have, however, not been defined. Calcium is known to be involved during fertilization of animal species. Increased intracellular free calcium, which can be achieved either by calcium influx or by mobilization of ions from intracellular stores, has been observed during activation of both eggs and sperm. A recent report by Bloodgood & Levin that gametes of C. reinhardii preloaded with 45Ca showed a transient increase in Ca efflux following mating, suggests that intracellular Ca redistribution may also accompany mating in this algal species. We have used X-ray microanalysis to analyze the subcellular distribution of bound calcium during mating in Chlamydomonas reinhardii. X-ray maps reveal that calcium is sequestered in discrete granules within the gamete cell body prior to mating and that during activation and cell fusion, calcium is diffuse throughout the cell. This suggests the possibility that calcium serves as a second messenger in this species. 相似文献
9.
Yu. A. Nikolaev 《Microbiology》2000,69(5):497-503
Exchange of information between bacteria via physical signals, referred to as “distant interactions” (DI), is the subject
of this review. All cases of DI reported to date are discussed, as well as the history of these studies and the place of DI
in bacterial communication. Bacterial DI are a particular case of DI occurring in nature (in plants, animals, and fungi).
Along with the chemical signals of intracellular communications, DI play a significant role in the life of microorganisms,
especially during critical and transitional periods. 相似文献
10.
Rapid Endocytosis and Vesicle Recycling in Neuroendocrine Cells 总被引:1,自引:0,他引:1
Endocytosis is a crucial process for neuroendocrine cells that ensures membrane homeostasis, vesicle recycling, and hormone
release reliability. Different endocytic mechanisms have been described in chromaffin cells, such as clathrin-dependent slow
endocytosis and clathrin-independent rapid endocytosis. Rapid endocytosis, classically measured in terms of a fast decrease
in membrane capacitance, exhibits two different forms, “rapid compensatory endocytosis” and “excess retrieval.” While excess
retrieval seems to be associated with formation of long-lasting endosomes, rapid compensatory endocytosis is well correlated
with exocytotic activity, and it is regarded as a mechanism associated to rapid vesicle recycling during normal secretory
activity. It has been suggested that rapid compensatory endocytosis may be related to the prevalence of a transient fusion
mode of exo-endocytosis. In the latter mode, the fusion pore, a nanometric-sized channel formed at the onset of exocytosis,
remains open for a few hundred milliseconds and later abruptly closes, releasing a small amount of transmitters. By this mechanism,
endocrine cell selectively releases low molecular weight transmitters, and rapidly recycles the secretory vesicles. In this
article, we discuss the cellular and molecular mechanisms that define the different forms of exocytosis and endocytosis and
their impact on vesicle recycling pathways. 相似文献
11.
Vassili V. Velkov 《Journal of biosciences》1999,24(4):529-559
This review is focused on the physiological and evolutionary strategies of the processes occurring during the entry of microbial
cells into stationary phase and the subsequent period of stasis. The molecular mechanisms adapting microorganisms from exponential
growth to a static state involve activation and complex regulation of the stationary factor Sigma-S, which directs RNA polymerase
to the specific promoters. As a result the static cells acquire general resistance (simultaneous tolerances) to different
environmental stresses. In parallel with the physiological adaptation to stasis, diverse genetical processes are aimed towards
resuming the growth of the static cells. Different types of mutagenesis occur: (i) in cells entering stasis and (ii) in static
cells (adaptive mutagenesis). Cessation of growth induces the transient hypermutator state resulting in the accumulation of
random mutations in the subpopulation of the static cells. If by chance, one or a few of such mutations lead to resumption
of division, the growing cell will return to a normal mechanism of spontaneous mutagenesis.
Another mechanism for generating genetical variability in stressed cells involves transposons and conjugative plasmids. Stresses
can stimulate the excision of some transposons, which, in turn, can generate chromosomal mutations and activate intracellular
mechanisms of mutagenesis. Under stress some conjugative plasmids activate genes encoding antirestriction proteins that repress
restriction-modification systems of the recipient cells. Moreover, under stress special cellular mechanisms decrease (alleviate)
the activity of restriction-modification systems which, in turn, enhance the probability of gene transfer into the stressed
cells.
Under stress, the efficiency of inter-species genetical barriers also decreases. This, stimulates inter-species gene transfer
and may lead to a burst of incipient speciation in the population of non-growing cells. After resumption of growth the genetical
barriers leading to isolation will be restored.
In general, the cessation of growth “switches on”, and resumption of growth “switches off”, a set of special processes that
are responsible for generating bursts of genetical variability in populations of microorganisms.
This article is dedicated to the memory of Nikolai V Timofeev-Ressovsky (1900–1981). 相似文献
12.
13.
Khandoker M. Morshed Kenneth E. McMartin 《In vitro cellular & developmental biology. Animal》1995,31(2):107-114
Summary Primary cultures of human proximal tubule (HPT) cells possess the characteristics of a tight epithelium and retain the characteristics
of in vivo renal function. HPT cells from confluent monolayers when grown on collagen-coated polycarbonate inserts in a hormonally
defined serum-free medium. However, initial studies of transepithelial transport observed large bidirectional fluxes of the
paracellular probe inulin. The present studies were designed to assess the transformation of HPT cell tight junctions to a
“leaky” state and subsequent recovery. The apparent transepithelial electrical resistance of HPT cells at confluence was 952.0±70.0
ohms*cm2, suggesting a well-developed tight junction-mediated paracellular pathway in this epithelium. However, replacement of the
growth media produced an immediate 90% drop in the initial resistance, which was paralleld by an increased flux of inulin
and of phenol red. This transient abolition of barrier function spontaneously reestablished over 1–2 h by a process that was
dependent on the ionic composition of the added media. Complete recovery of cellular resistance was paralleled by markedly
decreased fluxes of inulin and of phenol red. The recovery of cellular barrier function was inhibited by cytochalasin B suggesting
an intracellular action, not a physical disruption of the monolayer. These results suggest that the tight junctions in these
cells appear to transiently produce a leaky state during removal of the media, but rearrange to a “tight conformation” when
incubated in the appropriate media. 相似文献
14.
It has been demonstrated by us and other authors that first nervous cells in developing larvae from various trochozoan groups
differentiate at the periphery. These pioneer neurons are distinguished by the set of characters. They are located outside
the forming central ganglia; outgrowing fibers of central neurons use their processes as a “scaffolding” transmitter expression
in these neurons is transient. On the one hand, pioneer neurons mark the “frame” of the adult nervous system and thus play
a limiting role. On the other hand, pioneering navigation provides possible mechanisms for evolutional plasticity of the nervous
system in adults. In addition, pioneer neurons can underlie functional adaptation of trochophore animals, which minimizes
fitness decrease during the transition from the larval to the adult form during metamorphosis. 相似文献
15.
Simon Silver 《Biometals》2011,24(3):379-390
Understanding of BioMetals developed basically from a starting point about 60 years ago to current mechanistic understanding
of the biological behavior of many metal ions from protein structural and functional studies. Figure 1 shows a Biochemical Periodic Table, element by element, with requirements, roles and biochemistry of the specific ions indicated.
With few exceptions, the biology is of the ions formed and not of the elemental state of each. Early BioMetals efforts defined
nutritional growth needs for animals, plants and microbes for inorganic “macro-nutrients” such as magnesium, calcium, potassium,
sodium, and phosphate and of “micronutrients” such as copper, iron, manganese and zinc. Surprises came early with regard to
microbes, for example the finding that Escherichia coli (then and now the standard microbial model) grows happily in the apparent
total absence of calcium, sodium, and chloride, which are certainly major animal nutrients. Some elements such as mercury
and arsenic are never required by living cells, but are always toxic, often at very low levels. Therefore, the division into
nutrient elements and toxic elements came soon. For most inorganic nutrients, excessive amounts can be toxic as well, for
example for copper and iron. 相似文献
16.
Experimental studies testifying to the presence of an interrelation between the physiological functions of the organism and
physical and chemical processes in nerves are discussed. Changes in some physical and chemical parameters observed both upon
elicited rhythmic excitation of nerves and during the spontaneous rhythmic activity of neurons are analyzed. Upon rhythmic
excitation, a complex of physical and chemical processes is triggered, and reversible structural and metabolic rearrangements
at the subcellular and molecular levels occur that do not take place during the generation of a single action potential. Thus,
only in conditions of rhythmic excitation of a nerve, it is possible to reveal those processes that provide excitation of
nerves in the organism. The future possibilities of the investigations combining the biophysical and physiological approaches
are substantiated. Characteristic changes in physicochemical parameters are observed in nerves during the generation of a
series of action potentials of different frequency and duration (“frequency dependence”) under normal physiological conditions,
as well as in extreme situations and in nerve pathology. The structural and metabolic rearrangements are directly related
to the mode of rhythmic excitation and proceed both in the course of rhythmic excitation and after its termination. Shown
also is participation of the basic components of the nervous trunk (axon, Schwann cell, myelin, subcellular organelles) in
the realization of rhythmic excitation. In the coordination of all processes involved in rhythmic excitation, the main role
is played by the systems of redistribution and transport of intercellular and intracellular calcium. The idea is put forward
that myelin of nerve fibers is not only an insulator, but also an “intercellular depot” of calcium and participates in the
redistribution of different ions. Thus, the rhythmic excitation is of great importance in the realization of some physiological
functions, the adaptation to changing conditions, the liquidation of consequences of paralogical processes, the formation
of mechanisms of “memory,” etc. 相似文献
17.
Efficient protein folding and quality control are essential for unperturbed cell viability. Defects in these processes may
lead to production of aberrant polypeptides that are either degraded leading to “loss-of-function” phenotypes, or deposited
in or outside cells leading to “gain-of-toxic-function” phenotypes. Elucidation of molecular mechanisms regulating folding
and quality control of newly synthesized polypeptides is therefore of greatest interest. Here we describe protocols for metabolic
labelling of transfected/infected mammalian cells with [35S]-methionine and [35S]-cysteine, for immunoisolation from detergent extracts of the selected model proteins and for the investigation of the model
polypeptide’s intracellular fate in response to chaperone-deletions or to cell exposure to folding or degradation inhibitors. 相似文献
18.
Christian R. McIntire Garabet Yeretssian Maya Saleh 《Apoptosis : an international journal on programmed cell death》2009,14(4):522-535
Two of the main challenges that multicellular organisms faced during evolution were to cope with invading microorganisms and
eliminate and replace dying cells. Our innate immune system evolved to handle both tasks. Key aspects of innate immunity are
the detection of invaders or tissue injury and the activation of inflammation that alarms the system through the action of
cytokine and chemokine cascades. While inflammation is essential for host resistance to infections, it is detrimental when
produced chronically or in excess and is linked to various diseases, most notably auto-immune diseases, auto-inflammatory
disorders, cancer and septic shock. Essential regulators of inflammation are enzymes termed “the inflammatory caspases”. They
are activated by cellular sensors of danger signals, the inflammasomes, and subsequently convert pro-inflammatory cytokines
into their mature active forms. In addition, they regulate non-conventional protein secretion of alarmins and cytokines, glycolysis
and lipid biogenesis, and the execution of an inflammatory form of cell death termed “pyroptosis”. By acting as key regulators
of inflammation, energy metabolism and cell death, inflammatory caspases and inflammasomes exert profound influences on innate
immunity and infectious and non-infectious inflammatory diseases.
Christian R. McIntire and Garabet Yeretssian have contributed equally to this review. 相似文献
19.
Creatine kinase (CK) isoenzymes are essential for storing, buffering and intracellular transport of “energy-rich” phosphate
compounds in tissues with fluctuating high energy demand such as muscle, brain and other tissues and cells where CK is expressed.
In brain and many non-muscle cells, ubiquitous cytosolic “brain-type” BB-CK and ubiquitous mitochondrial CK (uMtCK) act as
components of a phosphocreatine shuttle to maintain cellular energy pools and distribute energy flux. To date, still relatively
little is known about direct coupling of functional dimeric BB-CK with other partner proteins or enzymes that are important
for cell function. Using a global yeast two-hybrid (Y2H) screen with monomeric B-CK as bait and a representative brain cDNA
library to search for interaction partners of B-CK with proteins of the brain, we repeatedly identified the cis-Golgi Matrix
protein (GM130) as recurrent interacting partner of B-CK. Since HeLa cells also express both BB-CK and GM130, we subsequently
used this cellular model system to verify and characterize the BB-CK-GM130 complex by GST-pulldown experiments, as well as
by in vivo co-localization studies with confocal microscopy. Using dividing HeLa cells, we report here for the first time that GM130
and BB-CK co-localize specifically in a transient fashion during early prophase of mitosis, when GM130 plays an important
role in Golgi fragmentation that starts also at early prophase. These data may shed new light on BB-CK function for energy
provision for Golgi-fragmentation that is initiated by cell signalling cascades in the early phases of mitosis. 相似文献
20.
E. M. McLachlan 《Neurophysiology》2007,39(4-5):251-258
The discharge of vasoconstrictor pathways arising in the CNS is largely unmodified as it passes through the sympathetic ganglia
to the vasculature. The underlying synaptic events have been revealed by intracellular recordings from sympathetic paravertebral
ganglion cells in the course of ongoing and reflex activity in anesthetized animals, first made in Skok’s Laboratory in Kyiv
(Ukraine). Each preganglionic neuron diverges to contact a number of post-ganglionic neurons, on each of which several pre-ganglionic
inputs converge. However, only suprathreshold “strong,” or “dominant” synapses are effective in transmitting the CNS signals.
Strong synapses differ from the other subthreshold “weak,” or “accessory” inputs: (a) excitatory synaptic currents are >1
nA in their amplitude, (b) 3 to ≈>30 times more quanta of acetylcholine are released, (c) pre-synaptic Ca2+ entry through channels resistant to all-known antagonists triggers acetylcholine release, and (d) post-synaptic Ca2+ entry boosts and prolongs the nicotinic current. While the majority of postganglionic neurons have only one strong input,
a proportion receives two or, rarely, three such inputs. In cells with multiple strong inputs, an equivalent number of discrete
Ca2+ currents can be evoked at distinct foci electrically distant from the soma, suggesting that each strong input has a unique
dendritic association with a cluster of Ca2+ channels. When strong preganglionic inputs are destroyed, residual weak synapses sprout and rapidly restore the suprathreshold
connections. While much remains to be discovered about how strong synapses are established, their high safety factor ensures
the wide and secure distribution of vasoconstrictor command signals from the CNS.
Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 294–301, July–October, 2007. 相似文献