scholarly journals IQ-Motif Proteins Influence Intracellular Free Ca2+ in Hippocampal Neurons Through Their Interactions With Calmodulin

2008 ◽  
Vol 99 (1) ◽  
pp. 264-276 ◽  
Author(s):  
Yoshihisa Kubota ◽  
John A. Putkey ◽  
Harel Z. Shouval ◽  
M. Neal Waxham
Keyword(s):  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Compartment Model ◽  
Buffering Capacity ◽  
Imaging Data ◽  
Iq Motif ◽  
Single Compartment Model ◽  
Intracellular Ca ◽  
Extrusion Mechanism ◽  
High Concentrations

Calmodulin (CaM) is most recognized for its role in activating Ca2+–CaM-dependent enzymes following increased intracellular Ca2+. However, CaM's high intracellular concentration indicates CaM has the potential to play a significant role as a Ca2+ buffer. Neurogranin (Ng) is a small neuronal IQ-motif–containing protein that accelerates Ca2+ dissociation from CaM. In cells that contain high concentrations of both Ng and CaM, like CA1 pyramidal neurons, we hypothesize that the accelerated Ca2+ dissociation from CaM by Ng decreases the buffering capacity of CaM and thereby shapes the transient dynamics of intracellular free Ca2+. We examined this hypothesis using a mathematical model constructed on the known biochemistry of Ng and confirmed the simulation results with Ca2+ imaging data in the literature. In a single-compartment model that contains no Ca2+ extrusion mechanism, Ng increased the steady-state free Ca2+. However, in the presence of a Ca2+ extrusion mechanism, Ng accelerated the decay rate of free Ca2+ through its ability to increase the Ca2+ dissociation from CaM, which in turn becomes subject to Ca2+ extrusion. Interestingly, PEP-19, another neuronal IQ-motif protein that accelerates both Ca2+ association and dissociation from CaM, appears to have the opposite impact than that of Ng on free Ca2+. As such, Ng may regulate, in addition to the Ca2+–CaM-dependent process, Ca2+-sensitive enzymes by influencing the buffering capacity of CaM and subsequently free Ca2+ levels. We examined the relative impact of these Ng-induced effects in the induction of synaptic plasticity.

scholarly journals BDNF Induces Calcium Elevations Associated With IBDNF, a Nonselective Cationic Current Mediated by TRPC Channels

2007 ◽  
Vol 98 (4) ◽  
pp. 2476-2482 ◽  
Author(s):  
Michelle D. Amaral ◽  
Lucas Pozzo-Miller
Keyword(s):  
Hippocampal Neurons ◽  
Transient Receptor Potential ◽  
Pyramidal Neurons ◽  
Receptor Potential ◽  
Trpc Channels ◽  
Hippocampal Pyramidal Neurons ◽  
Cationic Current ◽  
Intracellular Ca ◽  
Transient Receptor ◽  
Nonselective Cationic Current

Brain-derived neurotrophic factor (BDNF) has potent actions on hippocampal neurons, but the mechanisms that initiate its effects are poorly understood. We report here that localized BDNF application to apical dendrites of CA1 pyramidal neurons evoked transient elevations in intracellular Ca2+ concentration, which are independent of membrane depolarization and activation of N-methyl-d-aspartate receptors (NMDAR). These Ca2+ signals were always associated with IBDNF, a slow and sustained nonselective cationic current mediated by transient receptor potential canonical (TRPC3) channels. BDNF-induced Ca2+ elevations required functional Trk and inositol-tris-phosphate (IP3) receptors, full intracellular Ca2+ stores as well as extracellular Ca2+, suggesting the involvement of TRPC channels. Indeed, the TRPC channel inhibitor SKF-96365 prevented BDNF-induced Ca2+ elevations and the associated IBDNF. Thus TRPC channels emerge as novel mediators of BDNF-induced intracellular Ca2+ elevations associated with sustained cationic membrane currents in hippocampal pyramidal neurons.

Ca2+ and filopodial responses to glutamate in cultured astrocytes and neurons

1992 ◽  
Vol 70 (S1) ◽  
pp. S206-S218 ◽  
Author(s):  
A. H. Cornell-Bell ◽  
P. G. Thomas ◽  
J. M. Caffrey
Keyword(s):  
Primary Culture ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Inorganic Ions ◽  
Apical Surface ◽  
Neuronal Responses ◽  
Ca1 Neurons ◽  
Cultured Astrocytes ◽  
Intracellular Ca ◽  
Ca3 Neurons

Neurons and glia exhibit complex homeostatic interactions via shared extracellular space which can involve metabolites, inorganic ions, and neurotransmitters. Focal application of glutamate to both human and rat central nervous system astrocytes in primary culture produced a rapid, transient increase in both cytoplasmic and nuclear Ca2+. These Ca2+ waves can propagate at up to 15–20 μm/s for long distances (millimetres) through the astrocyte syncitium. Oscillatory Ca2+ signals were frequently observed under control conditions and were enhanced by glutamate application. These Ca2+ signals were paralleled by rapid extensions of filopodia from the astrocyte cell margin and apical surface near the point of glutamate application. Focal application of glutamate to rat hippocampal neurons also elicited rapid, transient increases in intracellular Ca2+. Levels of Ca2+ signals were consistently two- to three-fold greater in pyramidal neurons cultured from CA1 than in those from CA3. Filopodial extension was extensive in CA1 neurons, but rare in CA3 neurons, and in either case observable only during the first few days of primary culture. Diversity of glial and neuronal responses to binding the glutamate receptors may reflect their roles in homeostatic interactions.Key words: glutamate, astrocytes, hippocampal neurons, Ca2+ signals, filopodia.

scholarly journals The Chloride Homeostasis of CA3 Hippocampal Neurons Is Not Altered in Fully Symptomatic Mepc2-null Mice

2021 ◽  
Vol 15 ◽  
Author(s):  
Yasmine Belaïdouni ◽  
Diabe Diabira ◽  
Jinwei Zhang ◽  
Jean-Charles Graziano ◽  
Francesca Bader ◽  
...  
Keyword(s):  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Neurodevelopmental Disorder ◽  
Reversal Potential ◽  
Wild Type ◽  
Chloride Homeostasis ◽  
Inhibitory Strength ◽  
Extrusion Mechanism ◽  
Ca3 Pyramidal Neurons ◽  
Chloride Extrusion

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused mainly by mutations in the MECP2 gene. Mouse models of RTT show reduced expression of the cation-chloride cotransporter KCC2 and altered chloride homeostasis at presymptomatic stages. However, whether these alterations persist to late symptomatic stages has not been studied. Here we assess KCC2 and NKCC1 expressions and chloride homeostasis in the hippocampus of early [postnatal (P) day 30–35] and late (P50–60) symptomatic male Mecp2-null (Mecp2–/y) mice. We found (i) no difference in the relative amount, but an over-phosphorylation, of KCC2 and NKCC1 between wild-type (WT) and Mecp2–/y hippocampi and (ii) no difference in the inhibitory strength, nor reversal potential, of GABAA-receptor-mediated responses in Mecp2–/y CA3 pyramidal neurons compared to WT at any stages studied. Altogether, these data indicate the presence of a functional chloride extrusion mechanism in Mecp2–/y CA3 pyramidal neurons at symptomatic stages.

An approach for comparative quantification of myocardial blood flow (0-15-H2O-PET), perfusion (Tc-99m-tetrofosmin-SPECT), and metabolism (F 18-FDG-PET)

2001 ◽  
Vol 40 (05) ◽  
pp. 164-171 ◽  
Author(s):  
B. Nowak ◽  
H.-J. Kaiser ◽  
S. Block ◽  
K.-C. Koch ◽  
J. vom Dahl ◽  
...  
Keyword(s):  
Blood Flow ◽  
Myocardial Blood Flow ◽  
Fdg Pet ◽  
Model Fitting ◽  
Compartment Model ◽  
Left Ventricular ◽  
Short Axis ◽  
New Approach ◽  
Single Compartment Model ◽  
Tissue Fraction

Summary Aim: In the present study a new approach has been developed for comparative quantification of absolute myocardial blood flow (MBF), myocardial perfusion, and myocardial metabolism in short-axis slices. Methods: 42 patients with severe CAD, referred for myocardial viability diagnostics, were studied consecutively with 0-15-H2O PET (H2O-PET) (twice), Tc-99m-Tetrofosmin 5PECT (TT-SPECT) and F-18-FDG PET (FDG-PET). All dato sets were reconstructed using attenuation correction and reoriented into short axis slices. Each heart was divided into three representative slices (base, rnidventricular, apex) and 18 ROIs were defined on the FDG PET images and transferred to the corresponding H2O-PET and TT-SPECT slices. TT-SPECT and FDG-PET data were normalized to the ROI showing maximum perfusion. MBF was calculated for all left-ventricular ROIs using a single-compartment-model fitting the dynamic H2O-PET studies. Microsphere equivalent MBF (MBF_micr) was calculated by multiplying MBF and tissue-fraction, a parameter which was obtained by fitting the dynamic H2O-PET studies. To reduce influence of viability only well perfused areas (>70% TT-SPECT) were used for comparative quantification. Results: First and second mean global MBF values were 0.85 ml × min-1 × g-1 and 0.84 ml × min-1 × g1, respectively, with a repeatability coefficient of 0.30 ml ÷ min-1 × gl. After sectorization mean MBF_micr was between 0.58 ml × min1 ÷ ml"1 and 0.68 ml × min-1 × ml"1 in well perfused areas. Corresponding TT-SPECT values ranged from 83 % to 91 %, and FDG-PET values from 91 % to 103%. All procedures yielded higher values for the lateral than the septal regions. Conclusion: Comparative quantification of MBF, MBF_micr, TT-SPECT perfusion and FDG-PET metabolism can be done with the introduced method in short axis slices. The obtained values agree well with experimentally validated values of MBF and MBF_micr.

scholarly journals Epipregnanolone as a Positive Modulator of GABAA Receptor in Rat Cerebellar and Hippocampus Neurons

Biomolecules ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 791
Author(s):  
Julia Bukanova ◽  
Elena Solntseva ◽  
Rodion Kondratenko ◽  
Eva Kudova
Keyword(s):  
Gabaa Receptor ◽  
Purkinje Cells ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Patch Clamp Technique ◽  
Dual Effect ◽  
Combined Application ◽  
Gabaa Receptor Antagonist ◽  
Positive Modulator ◽  
Endogenous Steroid

Epipregnanolone (3β-hydroxy-5β-pregnan-20-one, Epi) is an endogenous steroid with important physiological effects and high affinity for GABAA receptors. The effect of Epi on GABA-induced chloride current (IGABA) in native neurons has hardly been studied. In this work, we studied the influence of Epi on the IGABA in the Purkinje cells of rat cerebellum and pyramidal neurons of rat hippocampus with the patch clamp technique. We showed that Epi is a positive modulator of the IGABA with EC50 of 5.7 µM in Purkinje cells and 9.3 µM in hippocampal neurons. Epi-induced potentiation of the IGABA was more potent at low vs. high GABA concentrations. Isopregnanolone (3β-hydroxy-5α-pregnan-20-one, Iso) counteracted Epi, reducing its potentiating effect by 2–2.3 times. Flumazenil, a nonsteroidal GABAA receptor antagonist, does not affect the Epi-induced potentiation. Comparison of the potentiating effects of Epi and allopregnanolone (3α-hydroxy-5α-pregnan-20-one, ALLO) showed that ALLO is, at least, a four times more potent positive modulator than Epi. The combined application of ALLO and Epi showed that the effects of these two steroids are not additive. We conclude that Epi has a dual effect on the IGABA increasing the current in the control solution and decreasing the stimulatory effect of ALLO.

Renal function measurements from MR renography and a simplified multicompartmental model

2007 ◽  
Vol 292 (5) ◽  
pp. F1548-F1559 ◽  
Author(s):  
Vivian S. Lee ◽  
Henry Rusinek ◽  
Louisa Bokacheva ◽  
Ambrose J. Huang ◽  
Niels Oesingmann ◽  
...  
Keyword(s):  
Low Dose ◽  
Random Noise ◽  
Compartment Model ◽  
Parameter Estimates ◽  
Imaging Data ◽  
Tracer Injection ◽  
Multicompartmental Model ◽  
Enhancement Curve ◽  
Reference Measurements ◽  
Single Kidney

The purpose of this study was to determine the accuracy and sources of error in estimating single-kidney glomerular filtration rate (GFR) derived from low-dose gadolinium-enhanced T1-weighted MR renography. To analyze imaging data, MR signal intensity curves were converted to concentration vs. time curves, and a three-compartment, six-parameter model of the vascular-nephron system was used to analyze measured aortic, cortical, and medullary enhancement curves. Reliability of the parameter estimates was evaluated by sensitivity analysis and by Monte Carlo analyses of model solutions to which random noise had been added. The dominant sensitivity of the medullary enhancement curve to GFR 1–4 min after tracer injection was supported by a low coefficient of variation in model-fit GFR values (4%) when measured data were subjected to 5% noise. These analyses also showed the minimal effects of bolus dispersion in the aorta on parameter reliability. Single-kidney GFR from MR renography analyzed by the three-compartment model (4.0–71.4 ml/min) agreed well with reference measurements from 99mTc-DTPA clearance and scintigraphy ( r = 0.84, P < 0.001). Bland-Altman analysis showed an average difference of 11.9 ml/min (95% confidence interval = 5.8–17.9 ml/min) between model and reference values. We conclude that a nephron-based multicompartmental model can be used to derive clinically useful estimates of single-kidney GFR from low-dose MR renography.

Fluid pressure modulates L-type Ca2+ channel via enhancement of Ca2+-induced Ca2+ release in rat ventricular myocytes

2008 ◽  
Vol 294 (4) ◽  
pp. C966-C976 ◽  
Author(s):  
Sunwoo Lee ◽  
Joon-Chul Kim ◽  
Yuhua Li ◽  
Min-Jeong Son ◽  
Sun-Hee Woo
Keyword(s):  
Ventricular Myocytes ◽  
Fluid Pressure ◽  
Inhibitory Effect ◽  
Cellular Mechanism ◽  
Confocal Imaging ◽  
Rat Ventricular Myocytes ◽  
Whole Cell Patch Clamp ◽  
Current Voltage ◽  
Intracellular Ca ◽  
High Concentrations

This study examines whether fluid pressure (FP) modulates the L-type Ca2+ channel in cardiomyocytes and investigates the underlying cellular mechanism(s) involved. A flow of pressurized (∼16 dyn/cm2) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes using a microperfusion method. The Ca2+ current ( ICa) and cytosolic Ca2+ signals were measured using a whole cell patch-clamp and confocal imaging, respectively. It was found that the FP reversibly suppressed ICa (by 25%) without altering the current-voltage relationships, and it accelerated the inactivation of ICa. The level of ICa suppression by FP depended on the level and duration of pressure. The Ba2+ current through the Ca2+ channel was only slightly decreased by the FP (5%), suggesting an indirect inhibition of the Ca2+ channel during FP stimulation. The cytosolic Ca2+ transients and the basal Ca2+ in field-stimulated ventricular myocytes were significantly increased by the FP. The effects of the FP on the ICa and on the Ca2+ transient were resistant to the stretch-activated channel inhibitors, GsMTx-4 and streptomycin. Dialysis of myocytes with high concentrations of BAPTA, the Ca2+ buffer, eliminated the FP-induced acceleration of ICa inactivation and reduced the inhibitory effect of the FP on ICa by ≈80%. Ryanodine and thapsigargin, abolishing sarcoplasmic reticulum Ca2+ release, eliminated the accelerating effect of FP on the ICa inactivation, and they reduced the inhibitory effect of FP on the ICa. These results suggest that the fluid pressure indirectly suppresses the Ca2+ channel by enhancing the Ca2+-induced intracellular Ca2+ release in rat ventricular myocytes.

scholarly journals Effects of Strontium on the Permeation and Gating Phenotype of Calcium Channels in Hair Cells

2008 ◽  
Vol 100 (4) ◽  
pp. 2115-2124 ◽  
Author(s):  
Adrian Rodriguez-Contreras ◽  
Ping Lv ◽  
Jun Zhu ◽  
Hyo Jeong Kim ◽  
Ebenezer N. Yamoah
Keyword(s):  
Hair Cell ◽  
Single Channel ◽  
Single Channels ◽  
Physiological Concentration ◽  
Closed State ◽  
Dependent Inactivation ◽  
Intracellular Ca ◽  
High Concentrations ◽  
Latency Distributions ◽  
Channel Properties

To minimize the effects of Ca2+ buffering and signaling, this study sought to examine single Ca2+ channel properties using Sr2+ ions, which substitute well for Ca2+ but bind weakly to intracellular Ca2+ buffers. Two single-channel fluctuations were distinguished by their sensitivity to dihydropyridine agonist (L-type) and insensitivity toward dihydropyridine antagonist (non-L-type). The L- and non-L-type single channels were observed with single-channel conductances of 16 and 19 pS at 70 mM Sr2+ and 11 and 13 pS at 5 mM Sr2+, respectively. We obtained KD estimates of 5.2 and 1.9 mM for Sr2+ for L- and non-L-type channels, respectively. At Ca2+ concentration of ∼2 mM, the single-channel conductances of Sr2+ for the L-type channel was ∼1.5 and 4.0 pS for the non-L-type channels. Thus the limits of single-channel microdomain at the membrane potential of a hair cell (e.g., −65 mV) for Sr2+ ranges from 800 to 2,000 ion/ms, assuming an ECa of 100 mV. The channels are ≥4-fold more sensitive at the physiological concentration ranges than at concentrations >10 mM. Additionally, the channels have the propensity to dwell in the closed state at high concentrations of Sr2+, which is reflected in the time constant of the first latency distributions. It is concluded that the concentration of the permeant ion modulates the gating of hair cell Ca2+ channels. Finally, the closed state/s that is/are altered by high concentrations of Sr2+ may represent divalent ion-dependent inactivation of the L-type channel.

Two Mechanisms That Raise Free Intracellular Calcium in Rat Hippocampal Neurons During Hypoosmotic and Low NaCl Treatment

2000 ◽  
Vol 83 (1) ◽  
pp. 81-89 ◽  
Author(s):  
Aren J. Borgdorff ◽  
George G. Somjen ◽  
Wytse J. Wadman
Keyword(s):  
Synaptic Transmission ◽  
Intracellular Calcium ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Cell Swelling ◽  
Tissue Slices ◽  
Extracellular Medium ◽  
Calcium Activity ◽  
Hippocampal Pyramidal Neurons

Previous studies have shown that exposing hippocampal slices to low osmolarity (πo) or to low extracellular NaCl concentration ([NaCl]o) enhances synaptic transmission and also causes interstitial calcium ([Ca2+]o) to decrease. Reduction of [Ca2+]o suggests cellular uptake and could explain the potentiation of synaptic transmission. We measured intracellular calcium activity ([Ca2+]i) using fluorescent indicator dyes. In CA1 hippocampal pyramidal neurons in tissue slices, lowering πo by ∼70 mOsm caused “resting” [Ca2+]i as well as synaptically or directly stimulated transient increases of calcium activity (Δ[Ca2+]i) to transiently decrease and then to increase. In dissociated cells, lowering πo by ∼70 mOsm caused [Ca2+]i to almost double on average from 83 to 155 nM. The increase of [Ca2+]i was not significantly correlated with hypotonic cell swelling. Isoosmotic (mannitol- or sucrose-substituted) lowering of [NaCl]o, which did not cause cell swelling, also raised [Ca2+]i. Substituting NaCl with choline-Cl or Na-methyl-sulfate did not affect [Ca2+]i. In neurons bathed in calcium-free medium, lowering πo caused a milder increase of [Ca2+]i, which was correlated with cell swelling, but in the absence of external Ca2+, isotonic lowering of [NaCl]o triggered only a brief, transient response. We conclude that decrease of extracellular ionic strength (i.e., in both low πo and low [NaCl]o) causes a net influx of Ca2+ from the extracellular medium whereas cell swelling, or the increase in membrane tension, is a signal for the release of Ca2+ from intracellular stores.

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