scholarly journals The Thermodynamically Expensive Contribution of Three Calcium Sources to Somatic Release of Serotonin

2021 ◽  
Author(s):  
Francisco F. De-Miguel
Keyword(s):  
Plasma Membrane ◽  
Action Potentials ◽  
Large Scale ◽  
Calcium Release ◽  
Atp Synthesis ◽  
Vesicle Transport ◽  
Thermodynamic Efficiency ◽  
Calcium Dependent ◽  
Calcium Sources ◽  
Frequency Of Action Potentials

The soma, dendrites and axon of neurons may display calcium-dependent release of transmitters and peptides. Such release is named extrasynaptic for occurring in the absence of synaptic structures. This review describes cooperative actions of three calcium sources on somatic exocytosis. Emphasis is given to the release of serotonin by the classical serotonergic leech Retzius neuron, which has allowed detailed studies of each step between excitation and exoctytosis. Trains of action potentials induce transmembrane calcium entry through L-type channels. If the frequency of action potentials is above 5 Hz, summation of calcium transients upon individual action potentials increases the intracellular calcium concentration to activate calcium–induced calcium release. The amplified calcium wave activates motochondrial ATP synthesis that fuels the transport of vesicles to the plasma membrane. Serotonin that is released activates autoreceptors coupled to phospholipase C. Production of IP3 produces release of calcium that sustains the large-scale exocytosis. The swiss-clock workings of the release machinery for somatic exocytosis has a striking disadvantage. The essential calcium-releasing endoplasmic reticulum that lays between resting vesicles and the plasma membrane becomes an obstacle for the vesicle transport. Such architecture reduces drastically the thermodynamic efficiency of the vesicle transport and elevates its energy cost..

A SIMPLE MODEL FOR INTERACTION OF VOLTAGE AND CALCIUM DYNAMICS IN VIRTUAL VENTRICULAR TISSUE

2003 ◽  
Vol 13 (12) ◽  
pp. 3873-3886
Author(s):  
O. V. ASLANIDI ◽  
A. V. HOLDEN
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Cell Model ◽  
Excitation Threshold ◽  
Calcium Dynamics ◽  
Variable Model ◽  
Ventricular Cell ◽  
Calcium Dependent ◽  
Intracellular Ca ◽  
A Site

A simple two-variable model is used to replace the formulation of calcium dynamics in the Luo–Rudy ventricular cell model. Virtual ventricular cell and tissue are developed and validated to reproduce restitution properties and calcium-dependent voltage patterns present in the original model. Basic interactions between the membrane potential and Ca 2+ dynamics in the virtual cell and a strand of the virtual tissue are studied. Intracellular calcium waves can be linked to both action potentials (APs) and delayed afterdepolarizations (DADs). An intracellular calcium wave propagating from the cell interior can induce an AP upon reaching the cell membrane. The voltage and the intracellular Ca 2+ patterns within the same cell can be highly desynchronized. In a one-dimensional strand of the virtual tissue calcium motion is driven by the AP propagation. However, calcium release can be induced upon certain conditions (e.g. Na + overload of the cells), which results in DADs propagating in the wake of AP. Such propagating DADs can reach the excitation threshold, generating a pair of extrasystolic APs. Collision of a propagating AP with a site of elevated intracellular Ca 2+ concentration does not affect the propagation under the normal conditions. Under Na + overload local elevation of the intracellular Ca 2+ leads to generation of an extrasystolic AP, which destroys the original propagating AP.

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Large-scale chromatographic purification of F1F0-ATPase and complex I from bovine heart mitochondria

1996 ◽  
Vol 318 (1) ◽  
pp. 343-349 ◽  
Author(s):  
Susan K BUCHANAN ◽  
John E. WALKER
Keyword(s):  
Complex I ◽  
Large Scale ◽  
Gel Filtration ◽  
Atp Synthesis ◽  
Lipid Vesicles ◽  
Proton Pumping ◽  
Heart Mitochondria ◽  
Nadh:Ubiquinone Oxidoreductase ◽  
Bovine Heart ◽  
F1fo Atpase

A new chromatographic procedure has been developed for the isolation of F1Fo-ATPase and NADH:ubiquinone oxidoreductase (complex I) from a single batch of bovine heart mitochondria. The method employed dodecyl β-Δ-maltoside, a monodisperse, homogeneous detergent in which many respiratory complexes exhibit high activity, for solubilization and subsequent purification by ammonium sulphate fractionation and column chromatography. A combination of anion-exchange, gel-filtration, and dye-ligand affinity chromatography was used to purify both complexes to homogeneity. The F1Fo-ATPase preparation contains only the 16 known subunits of the enzyme. It has oligomycin-sensitive ATP hydrolysis activity and, as demonstrated elsewhere, when reconstituted into lipid vesicles it is capable of ATP-dependent proton pumping and of ATP synthesis driven by a proton gradient [Groth and Walker (1996) Biochem. J. 318, 351–357]. The complex I preparation contains all of the subunits identified in other preparations of the enzyme, and has rotenone-sensitive NADH:ubiquinone oxidoreductase and NADH:ferricyanide oxidoreductase activities. The procedure is rapid and reproducible, yielding 50–80 mg of purified F1Fo-ATPase and 20–40 mg of purified complex I from 1 g of mitochondrial membranes. Both preparations are devoid of phospholipids, and gel filtration and dynamic light scattering experiments indicate that they are monodisperse. Therefore, the preparations fulfil important prerequisites for structural analysis.

scholarly journals Calcium-dependent fusion of the plasma membrane fraction from human neutrophils with liposomes

1990 ◽  
Vol 1025 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Joseph W. Francis ◽  
James E. Smolen ◽  
Kenneth J. Balazovich ◽  
Rebecca R. Sandborg ◽  
Laurence A. Boxer
Keyword(s):  
Plasma Membrane ◽  
Membrane Fraction ◽  
Human Neutrophils ◽  
Plasma Membrane Fraction ◽  
Calcium Dependent

Abstract 272: Sex Differences in β-Adrenergic Responsiveness of Excitation-Contraction Coupling in Isolated Rabbit Hearts

2014 ◽  
Vol 115 (suppl_1) ◽  
Author(s):  
Gregory Hoeker ◽  
Ashleigh Hood ◽  
Rodolphe Katra ◽  
Steven Poelzing ◽  
Steven Pogwizd
Keyword(s):  
Sex Differences ◽  
Action Potentials ◽  
Adrenergic Receptor ◽  
Calcium Release ◽  
Dependent Manner ◽  
Ectopic Activity ◽  
Dose Threshold ◽  
Ectopic Beats ◽  
Cardioprotective Effects ◽  
Dose Dependent

Introduction: Sex differences in β-adrenergic receptor (β-AR) responsiveness are associated with female cardioprotection. We hypothesize that female (F) rabbits have reduced responsiveness to β-AR stimulation vs males (M), and that the degree and type of sex differences vary with the β-AR subtypes that are activated. Methods: Ventricular action potentials (AP) and intracellular calcium transients (CaT) were optically mapped from the epicardial surface of rabbit hearts during 3 Hz pacing. Spontaneous calcium release (SCR) and ectopic activity were elicited at 1, 3, and 5.5 Hz. β-responsiveness was assessed with the nonselective β-agonist isoproterenol (Iso, 1-316 nM), or β2-AR selective agonist zinterol (Zin, 10 nM). Results: At baseline, the time constant of CaT decay (τ) was faster in F than M (54.0±1.7 vs 62.1±3.0 ms; n=14, 14; p < 0.05), with no sex difference in CaT duration (CaD80). AP duration (APD90) was shorter in F than M (202.5±5.0 vs 218.2±5.7 ms; p < 0.05). Iso decreased τ, CaD80, and APD90 in a dose-dependent manner in both sexes (n = 5, 5 for F, M). Iso decreased τ to a lesser extent in F than M for 1 and 32-316 nM Iso (F = 11-32 ms, M = 23-48 ms; p < 0.05). The Iso-induced decrease in CaD80 was not significantly different in F than M at any dose. The Iso-induced decrease in APD90 was significantly less in F than M only at 316 nM Iso (75.5±8.7 ms vs 103.9±6.2 ms, p < 0.05). In contrast, there were no sex differences in the response to Zin for τ, CaD80, or APD90 (n = 6, 6 for F, M). Zin decreased τ by 7.2±2.0 ms in F vs 12.7±3.7 ms in M; CaD80 by 18.0±5.3% in F vs 21.1±8.0 ms in M; and APD90 by 24.9±8.5 ms in F vs 21.9±8.9 ms in M. SCR was observed in 50% (6/12) of hearts treated with Zin, whereas Iso elicited SCR in all hearts (10/10) with a dose threshold of 32 nM. No ectopic beats were observed with Zin (0/36 trials in 12 hearts). With Iso, ectopic activity was less frequent in F hearts (16%, 12/75 trials in 5 hearts) than in M hearts (41%, 26/68 trials in 5 hearts, p < 0.05). Conclusions: These results suggest that sex differences in AP and CaT depend on the dose of the agonist used and the β-AR subtypes that are activated. Elucidating nuances of sex differences in β-AR subtype physiology will provide a better understanding of the mechanisms of reduced β-responsiveness in F and its cardioprotective effects.

Investigation of the role of microtubules in protein secretion from lactating mouse mammary epithelial cells

1992 ◽  
Vol 102 (2) ◽  
pp. 239-247 ◽  
Author(s):  
M.E. Rennison ◽  
S.E. Handel ◽  
C.J. Wilde ◽  
R.D. Burgoyne
Keyword(s):  
Plasma Membrane ◽  
Epithelial Cells ◽  
Protein Secretion ◽  
Secretory Pathway ◽  
Mammary Epithelial Cells ◽  
Early Stage ◽  
Major Effect ◽  
Vesicle Transport ◽  
Mammary Epithelial ◽  
Mammary Cells

Disruption of microtubules has been shown to reduce protein secretion from lactating mammary epithelial cells. To investigate the involvement of microtubules in the secretory pathway in these cells we have examined the effect of nocodazole on protein secretion from mammary epithelial cells derived from the lactating mouse. Mouse mammary cells have extensive microtubule networks and 85% of their tubulin was in a polymeric form. Treatment with 1 micrograms/ml nocodazole converted most of the tubulin into a soluble form. In a continuous labelling protocol it was found that nocodazole did not interfere with protein synthesis but over a 5 h period secretion was markedly inhibited. To determine whether the inhibition was at the level of early or late stages of the secretory pathway mammary cells were pulse-labelled for 1 h to label protein throughout the secretory pathway before nocodazole treatment. When secretion was subsequently assayed it was found to be slower and only partially inhibited. These findings suggest that the major effect of nocodazole is on an early stage of the secretory pathway and that microtubules normally facilitate vesicle transport to the plasma membrane. An involvement of microtubules in vesicle transport to the plasma membrane is consistent with an observed accumulation of casein vesicles in nocodazole-treated cells. Exocytosis stimulated by the calcium ionophore ionomycin was unaffected by nocodazole treatment. We conclude from these results that the major effect of nocodazole is at an early stage of the secretory pathway, one possible target being casein vesicle biogenesis in the trans-Golgi network.

scholarly journals Large-scale purification of presynaptic plasma membranes from Torpedo marmorata electric organ.

1985 ◽  
Vol 101 (5) ◽  
pp. 1757-1762 ◽  
Author(s):  
N Morel ◽  
J Marsal ◽  
R Manaranche ◽  
S Lazereg ◽  
J C Mazie ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Large Scale ◽  
Plasma Membranes ◽  
Electric Organ ◽  
Acetylcholinesterase Activity ◽  
Cholinergic Nerve Terminals ◽  
Membrane Bound ◽  
Torpedo Electric Organ ◽  
Presynaptic Plasma Membrane ◽  
Glycera Convoluta

The presynaptic plasma membrane (PSPM) of cholinergic nerve terminals was purified from Torpedo electric organ using a large-scale procedure. Up to 500 g of frozen electric organ were fractioned in a single run, leading to the isolation of greater than 100 mg of PSPM proteins. The purity of the fraction is similar to that of the synaptosomal plasma membrane obtained after subfractionation of Torpedo synaptosomes as judged by its membrane-bound acetylcholinesterase activity, the number of Glycera convoluta neurotoxin binding sites, and the binding of two monoclonal antibodies directed against PSPM. The specificity of these antibodies for the PSPM is demonstrated by immunofluorescence microscopy.

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