scholarly journals Inositol 1,4,5-trisphosphate-induced calcium release in the organelle layers of the stratified, intact egg of Xenopus laevis.

1990 ◽  
Vol 110 (4) ◽  
pp. 1103-1110 ◽  
Author(s):  
J K Han ◽  
R Nuccitelli
Keyword(s):  
Xenopus Laevis ◽  
Time Course ◽  
Calcium Release ◽  
The Other ◽  
Dependent Manner ◽  
Subsequent Removal ◽  
Independent Manner ◽  
Physiological Conditions ◽  
Inositol 1,4,5 Trisphosphate ◽  
Kinetics Of

Using double-barreled, Ca2(+)-sensitive microelectrodes, we have examined the characteristics of the Ca2+ release by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) in the various layers of Xenopus laevis eggs in which the organelles had been stratified by centrifugation. Centrifugation of living eggs stratifies the organelles yet retains them in the normal cytoplasmic milieu. The local increase in intracellular free Ca2+ in each layer was directly measured under physiological conditions using theta-tubing, double-barreled, Ca2(+)-sensitive microelectrodes in which one barrel was filled with the Ca2+ sensor and the other was filled with Ins(1,4,5)P3 for microinjection. The two tips of these electrodes were very close to each other (3 microns apart) enabling us to measure the kinetics of both the highly localized intracellular Ca2+ release and its subsequent removal in response to Ins(1,4,5)P3 injection. Upon Ins(1,4,5)P3 injection, the ER-enriched layer exhibited the largest release of Ca2+ in a dosage-dependent manner, whereas the other layers, mitochondria, lipid, and yolk, released 10-fold less Ca2+ in a dosage-independent manner. The removal of released Ca2+ took place within approximately 1 min. The sensitivity to Ins(1,4,5)P3 and the time course of intracellular Ca2+ release in the unstratified (unactivated) egg is nearly identical to that observed in the ER layer of the stratified egg. Our data suggest that the ER is the major organelle of the Ins(1,4,5)P3-sensitive Ca2+ store in the egg of Xenopus laevis.

Calcium removal kinetics of the sarcoplasmic reticulum ATPase in skeletal muscle

1997 ◽  
Vol 272 (4) ◽  
pp. C1087-C1098 ◽  
Author(s):  
E. E. Burmeister Getz ◽  
S. L. Lehman
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Initial Rate ◽  
Troponin C ◽  
The Other ◽  
Physiological Conditions ◽  
Initial Binding ◽  
Kinetics Of ◽  
Transient And Steady State

The models of the sarcoplasmic reticulum (SR) Ca pump used to simulate Ca kinetics in muscle fibers are simple but inconsistent with data on Ca binding or steady-state uptake. We develop a model of the SR pump that is consistent with data on transient and steady-state Ca removal and has rate constants identified under near-physiological conditions. We also develop models of the other main Ca-binding proteins in skeletal muscle: troponin C and parvalbumin. These models are used to simulate Ca transients in cut fibers during and after depolarizing pulses. Simulations using the full SR pump model are contrasted with simulations using a Michaelis-Menten (MM) approximation to SR pump kinetics. The MM pump underestimates the amount of Ca released during depolarization, underestimates the initial rate of Ca binding by the pump, and overestimates the later rate of Ca pumping. These errors are due to fast initial binding by the SR pump, which is neglected in the MM approximation.

scholarly journals Dynamics of aminopyridine block of potassium channels in squid axon membrane.

1976 ◽  
Vol 68 (5) ◽  
pp. 519-535 ◽  
Author(s):  
J Z Yeh ◽  
G S Oxford ◽  
C H Wu ◽  
T Narahashi
Keyword(s):  
Time Course ◽  
Membrane Surface ◽  
K Channel ◽  
Dependent Manner ◽  
Squid Axon ◽  
Axon Membrane ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Aminopyridines (2-AP, 3-AP, and 4-AP) selectively block K channels of squid axon membranes in a manner dependent upon the membrane potential and the duration and frequency of voltage clamp pulses. They are effective when applied to either the internal or the external membrane surface. The steady-state block of K channels by aminopyridines is more complete for low depolarizations, and is gradually relieved at higher depolarizations. The K current in the presence of aminopyridines rises more slowly than in control, the change being more conspicuous in 3-AP and 4-AP than in 2-AP. Repetitive pulsing relieves the block in a manner dependent upon the duration and interval of pulses. The recovery from block during a given test pulse is enhanced by increasing the duration of a conditioning depolarizing prepulse. The time constant for this recovery is in the range of 10-20 ms in 3-AP and 4-AP, and shorter in 2-AP. Twin pulse experiments with variable pulse intervals have revealed that the time course for re-establishment of block is much slower in 3-AP and 4-AP than in 2-AP. These results suggest that 2-AP interacts with the K channel more rapidly than 3-AP and 4-AP. The more rapid interaction of 2-AP with K channels is reflected in the kinetics of K current which is faster than that observed in 3-AP or 4-AP, and in the pattern of frequency-dependent block which is different from that in 3-AP or 4-AP. The experimental observations are not satisfactorily described by alterations of Hodgkin-Huxley n-type gating units. Rather, the data are consistent with a simple binding scheme incorporating no changes in gating kinetics which conceives of aminopyridine molecules binding to closed K channels and being released from open channels in a voltage-dependent manner.

scholarly journals Block of current through single calcium channels by Fe, Co, and Ni. Location of the transition metal binding site in the pore.

1991 ◽  
Vol 97 (2) ◽  
pp. 351-367 ◽  
Author(s):  
B D Winegar ◽  
R Kelly ◽  
J B Lansman
Keyword(s):  
Metal Binding ◽  
The Other ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Coulombic Interactions ◽  
Rate Limiting Step ◽  
Ion Size ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Ca2 Channels

The blocking actions of Fe2+, Co2+, and Ni2+ on unitary currents carried by Ba2+ through single dihydropyridine-sensitive Ca2+ channels were recorded from cell-attached patches on myotubes from the mouse C2 cell line. Adding millimolar concentrations of blocker to patch electrodes containing 110 mM BaCl2 produced discrete excursions to the closed channel level. The kinetics of blocking and unblocking were well described with a simple model of open channel block. Hyperpolarization speeded the exit of all of the blockers from the channel, as expected if the blocking site resides within the pore. The block by Ni2+ differs from that produced by Fe2+ and Co2+ because Ni2+ enters the channel approximately 20 times more slowly and exits approximately 50 times more slowly. Ni2+ also differs from the other transition metals because at millimolar concentrations it reduces the amplitude of the unitary current in a concentration-dependent manner. The results are consistent with the idea that the rate-limiting step for ion entry into the channel is water loss at its inner coordination sphere; unblocking, on the other hand, cannot be explained in terms of simple coulombic interactions arising from differences in ion size.

scholarly journals “The flavor enhancer maltol increases pigment aggregation in dermal and neural melanophores in Xenopus laevis tadpoles”

2019 ◽  
Author(s):  
Lara I. Dahora ◽  
Ashley Fitzgerald ◽  
Matthew Emanuel ◽  
Alexa F. Baiges ◽  
Zahabiya Husain ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Time Course ◽  
Dependent Manner ◽  
Adaptation Mechanism ◽  
Toxicological Effect ◽  
Similar Dose ◽  
Dynamic Cell ◽  
Pigment Aggregation ◽  
Dose Dependent ◽  
Flavor Enhancer

ABSTRACTMelanophores are pigmented cells that change the distribution of pigmented melanosomes, enabling animals to appear lighter or darker for camouflage, thermoregulation, and UV-protection. A complex series of hormonal and neural mechanisms regulates melanophore pigment distribution, making these cells a valuable tool to screen toxicants as a dynamic cell type that responds rapidly to the environment. We found that maltol, a naturally occurring flavor enhancer and fragrance agent, induces melanophore pigment aggregation in a dose-dependent manner in Xenopus laevis tadpoles. To determine if maltol affects camouflage adaptation, we placed tadpoles into maltol baths situated over either white or black background. Maltol induced pigment aggregation in a similar dose-dependent pattern regardless of background color. We also tested how maltol treatment compares to melatonin treatment and found that the degree of pigment aggregation induced by maltol is similar to treatment with melatonin, but the time course differs significantly. Last, maltol had no effect on mRNA expression of pro-opiomelanocortin or melanin concentrating hormone receptor in the brain, both of which regulate camouflage-related pigment aggregation. Our results suggest that maltol does not exert its effects via the camouflage adaptation mechanism nor via melatonin-based mechanisms. These results are the first to identify a specific toxicological effect of maltol exposure and rules out several mechanisms by which maltol may exert its effects on pigment aggregation.

Mechanisms of intracellular calcium release during hormone and neurotransmitter action investigated with flash photolysis

1993 ◽  
Vol 184 (1) ◽  
pp. 105-127
Author(s):  
D. C. Ogden ◽  
K. Khodakhah ◽  
T. D. Carter ◽  
P. T. Gray ◽  
T. Capiod
Keyword(s):  
Time Course ◽  
Calcium Release ◽  
Flash Photolysis ◽  
Single Cells ◽  
Cell Types ◽  
Peripheral Tissues ◽  
Perfusion Studies ◽  
Kinetics Of ◽  
Purkinje Neurones ◽  
Fast Perfusion

To understand the complex time course of cytosolic Ca2+ signalling evoked by hormones and neurotransmitters, it is necessary to know the kinetics of steps in the second-messenger cascade, particularly cooperative and inhibitory interactions between components that might give rise to periodic fluctuations. In the case of inositol trisphosphate (InsP3)-evoked Ca2+ release, fast perfusion studies with subcellular fractions or permeabilised cells can be made if sufficient homogeneous tissue is available. Single-cell studies can be made by combining whole-cell patch-clamp techniques and microspectrofluorimetry with flash photolytic release of InsP3 to give quantitative, time-resolved data of Ca2+ release from stores. A technical description is given here of flash photolysis of caged InsP3, and the results of fast perfusion and flash photolytic experiments are reviewed. Studies of kinetics of Ca2+ release have shown that the InsP3 receptor/channel is regulated first by positive and then by negative feedback by free cytosolic Ca2+ concentration, producing a pulse of Ca2+ release having properties that may be important in the spatial propagation of Ca2+ signals within and between cells. The properties of InsP3-evoked Ca2+ release in single cells differ between peripheral tissues, such as the liver, and Purkinje neurones of the cerebellum. Purkinje neurones need 20–50 times higher InsP3 concentrations and release Ca2+ to change the free cytosolic concentration 30 times faster and to higher peak concentrations than in liver. The InsP3 receptors in the two cell types appear to differ in apparent affinity, and the greater Ca2+ efflux from stores in Purkinje cells is probably due to a high receptor density.

CD200-, CX3CL1-, and TREM2-mediated neuron-microglia interactions and their involvements in Alzheimer’s disease

2018 ◽  
Vol 29 (8) ◽  
pp. 837-848 ◽  
Author(s):  
Lihang Zhang ◽  
Juan Xu ◽  
Jinchao Gao ◽  
Yuncheng Wu ◽  
Ming Yin ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Central Nervous System ◽  
Dependent Manner ◽  
Independent Manner ◽  
Physiological Conditions ◽  
The Central Nervous System ◽  
And Function ◽  
Cluster Of Differentiation ◽  
The Brain

Abstract Neurons and microglia are two major components in the central nervous system (CNS). The interactions between them play important roles in maintaining homeostasis of the brain. In recent years, substantial studies have focused on the interactions between neurons and microglia, revealing that microglia become reactive when the interactions are pathophysiologically interfered, usually accompanying neuronal injury, which is a common feature for Alzheimer’s disease (AD). Many molecules and factors participate in these physiological and pathological processes, either in a contact-dependent or a contact-independent manner. Accumulating studies have revealed that in the CNS, cluster of differentiation-200 (CD200) and fractalkine (CX3CL1) expressed mainly on neurons and triggering receptor expressed on myeloid cells 2 (TREM2) expressed mainly on microglia. These molecules can mediate neuron-microglia interactions in a contact-dependent manner and contribute to the pathogenesis of AD. Here, we review the expression, distribution, and function of CD200, CX3CL1, and TREM2 in regulating neuron-microglia interactions under physiological conditions as well as in AD.

scholarly journals Kinetics of Immune Responses to Influenza Virus-Like Particles and Dose-Dependence of Protection with a Single Vaccination

2009 ◽  
Vol 83 (9) ◽  
pp. 4489-4497 ◽  
Author(s):  
Fu Shi Quan ◽  
Dae-Goon Yoo ◽  
Jae-Min Song ◽  
John D. Clements ◽  
Richard W. Compans ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Immune Responses ◽  
Neutralizing Antibodies ◽  
Time Course ◽  
Protective Efficacy ◽  
Dependent Manner ◽  
Lethal Challenge ◽  
Promising Alternative ◽  
Virus Like Particles ◽  
Kinetics Of

ABSTRACT The format of influenza virus-like particles (VLPs) as a nonreplicating particulate vaccine candidate is a promising alternative to conventional egg-based vaccines. In this study, we have investigated the detailed kinetics of immune responses and protective efficacy after a single intranasal immunization with different doses of VLPs alone or in the presence of an Escherichia coli mutant heat-labile enterotoxin [mLT(R192G)] or cholera toxin subunit B as adjuvants. Analysis of immune responses showed differential kinetics in a VLP antigen dose-dependent manner and dynamic changes in the ratios of antibody immunoglobulin G isotypes over the time course. Protection against lethal challenge was observed with a single immunization with influenza VLPs even without adjuvant. The addition of adjuvant showed significant antigen-sparing effects with improved protective efficacy. The protective immune responses, efficacies of protection, and antigen-sparing effects were significantly improved by a second immunization as determined by the levels of neutralizing antibodies, morbidity postchallenge, lung viral titers, and inflammatory cytokines. Our results are informative for a better understanding of the protective immunity induced by a single dose or two doses of influenza VLPs, which is dependent on antigen dosage and the presence of adjuvant, and will provide insights into designing effective vaccines based on VLPs.

Effort Choices between Group and Individual Tasks in Mixed Incentives

2017 ◽  
Vol 30 (1) ◽  
pp. 203-217
Author(s):  
Yu Tian ◽  
Brad M. Tuttle ◽  
Robert A. Leitch
Keyword(s):  
Systems Design ◽  
Data Availability ◽  
The Other ◽  
Dependent Manner ◽  
Incentive Systems ◽  
Individual Group ◽  
Independent Manner ◽  
Group Incentives ◽  
Total Effort

ABSTRACT Mixed individual and group incentives are widely used in practice under the assumption that by incentivizing both, organizations can increase total effort and predictably direct effort. The present paper explores these assumptions under two forms of mixed incentives, one in which incentives are implemented in a simultaneous/independent manner and the other in a sequential/dependent manner. Results suggest that adding individual incentives to group incentives motivates greater total effort, but adding group incentives to individual incentives does not, regardless of the structure or amount of the mixed incentives. We also find that the independent mixed incentives in our setting lead individuals to allocate a greater (less) percentage of total effort to individual (group) tasks than the sequential mixed incentives. Our findings have important implications to incentive systems design by suggesting that organizations need to consider a fit between the incentives and where they would like their employees to allocate effort. Data Availability: Data are available on request.

Perifused adenohypophyseal cells: release of ACTH and kinetics of the response to secretagogues

1983 ◽  
Vol 61 (5) ◽  
pp. 488-494
Author(s):  
John Randle ◽  
Marian Jutisz
Keyword(s):  
Mode Of Action ◽  
Intracellular Transport ◽  
Time Course ◽  
The Other ◽  
Release Process ◽  
Corticotrophin Releasing Factor ◽  
Course Of Action ◽  
Frequent Sampling ◽  
Kinetics Of ◽  
Perifusion System

The release of ACTH-like immunoactivity (ACTH-LI) from perifused dispersed adenohypophyseal cells was examined under basal conditions and in response to various secretagogues. Frequent sampling of effluent perifusion medium and a variable stimulation format allowed us to discern differences in the effects of the secretagogues. The dye, dextran blue, was used to define the kinetics of flow intrinsic to the perifusion system, allowing a detailed analysis of the responses to secretagogues. Each agent had a time course of action which could be related to its supposed site and mode of action in these cells. A crude hypothalamic extract, a partially purified corticotrophin releasing factor preparation, 8-bromoadenosine 3′,5′-cyclic monophosphate (8Br-cAMP), and 3-isobutyl-1-methylxanthine all caused dose-related, repeatable increases of the release of ACTH-LI. A 10-fold elevation in the concentration of K+ in the perifusion medium (10K) caused a transient increase in the release of ACTH-LI which was reduced when repeated. These results suggest that 10K stimulates the release of ACTH-LI only from a "readily-releaseable pool." The other agents appear to affect the release process more profoundly, for example, by stimulating intracellular transport of the ACTH-LI.

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