scholarly journals Neuromuscular junction instability and altered intracellular calcium handling as early determinants of force loss during unloading in humans

2021 ◽  
Author(s):  
Elena Monti ◽  
Carlo Reggiani ◽  
Martino V. Franchi ◽  
Luana Toniolo ◽  
Marco Sandri ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Intracellular Calcium ◽  
Calcium Handling

Abstract MP135: Cardiac Sarcoplasmic Reticulum Calcium Cycling is Regulated by Kinase Independent Function of Pi3kgamma

2020 ◽  
Vol 127 (Suppl_1) ◽  
Author(s):  
Maradumane L Mohan ◽  
Conner P Witherow ◽  
Robert S Papay ◽  
Sathyamangla V Naga Prasad
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Cardiac Contractility ◽  
Underlying Mechanism ◽  
Calcium Handling ◽  
Ventricular Contractility ◽  
Independent Function ◽  
Calcium Cycling ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Phosphoinositide 3 Kinase

Genetic deletion of Phosphoinositide 3-kinase (PI3Kγ) in mice (PI3Kγ -/- ) results in increased cAMP levels and enhanced ventricular contractility. We investigated whether the lack of PI3Kγ plays a role in cardiac contractility by altering intracellular calcium recycling. Isolated cardiomyocytes from PI3Kγ -/- mice showed significantly reduced calcium reuptake by sarcoendoplasmic reticulum (SR) following caffeine induced calcium release indicating that PI3Kγ locally regulates the function of SR. The intracellular calcium remained at elevated levels in the cardiomyocytes of PI3Kγ -/- for a prolonged period after caffeine treatment. This could be due to changes in phosphorylation of SERCA2, Ryanodine receptor (RyR 2 ) or phospholamban (PLN). In fact, when we looked at phosphorylation of PLN in cardiac lysates, a major regulator of cardiac contractility and relaxation, PI3Kγ -/- mice showed significantly reduced PLN phosphorylation compared to littermate controls. Previous studies from our laboratory suggested that absence of PI3Kγ leads to increase in protein phosphatase (PP) activity which could be possible reason for rapid dephosphorylation of PLN, resulting in inhibition of SERCA2 pump. We observed increased SR associated PP activity and PLN associated PP activity in PI3Kγ -/- mice. We also observed increased association of PP-1 and PP2A with PLN in the absence of PI3Kγ. The altered calcium handling in the cardiomyocytes of PI3Kγ -/- mice could be restored to the level of WT controls by okadaic acid mediated inhibition of PP, suggesting that PI3Kγ plays a role in regulating PP activity associated with SR. To test whether PI3Kγ activity is required for PLN dephosphorylation and SR calcium cycling, we used mice with cardiac specific overexpression of kinase dead PI3Kγ (PI3Kγ inact ) in global PI3Kγ -/- mice (PI3Kγ inact /PI3Kγ -/- ). PI3Kγ inact /PI3Kγ -/- mice showed restored PLN phosphorylation, improved caffeine induced calcium reuptake, decreased SR and PLN associated PP activity. These studies show a novel regulation of PP and SR calcium regulation by kinase independent function of PI3Kγ. The underlying mechanism of PP regulation by PI3Kγ will be presented.

P943The effects of ovariectomy on guinea pig cardiomyocyte intracellular calcium regulation and phosphorylation

EP Europace ◽  
2020 ◽  
Vol 22 (Supplement_1) ◽  
Author(s):  
E Ching ◽  
J M Firth ◽  
A J Francis ◽  
N Islam ◽  
K T Macleod
Keyword(s):  
Intracellular Calcium ◽  
Calcium Regulation ◽  
Left Ventricular ◽  
Calcium Handling ◽  
Time To Peak ◽  
Oestrogen Deficiency ◽  
Calcium Handling Proteins ◽  
Presence And Absence ◽  
Intracellular Calcium Regulation

Abstract Background Differences in cardiovascular disease risk between men and women have been partly attributed to the cardioprotective effects of oestrogen. Long-term oestrogen deficiency has been shown to alter cardiomyocyte intracellular calcium handling, but little is known about the mechanisms by which these changes occur. Oestrogen is thought to induce both genomic and non-genomic effects on cardiomyocytes, the latter including phosphorylation of calcium handling proteins. Purpose This study addresses the hypothesis that long-term oestrogen deficiency increases protein kinase A (PKA) and calcium/calmodulin-dependent kinase II (CaMKII) phosphorylation in cardiomyocytes, resulting in altered intracellular calcium regulation. Methods Female guinea pigs underwent sham (n = 7) or ovariectomy (OVx) (n = 8) operations and 150 days later, left ventricular myocytes were enzymatically isolated and loaded with fluo-4AM to monitor intracellular calcium. Calcium transients (CaT) were recorded using confocal microscopy. PKA and CaMKII phosphorylation were inhibited by superfusing cells with specific inhibitors, PKI and AIP, respectively. Experiments were carried out both in the presence and absence of β-agonist, isoprenaline (ISO), and relative changes to CaT parameters compared between OVx and sham cells. Results CaT amplitude was greater (p < 0.05) in the OVx group (ΔF/Fo= 2.51 ± 0.57) compared with sham (ΔF/Fo = 2.16 ± 0.57). Inhibition of CaMKII phosphorylation increased CaT amplitude in the sham but not OVx group, both in the presence (by 22%, p < 0.01) and absence of ISO (by 19%, p < 0.01). Time to peak of the CaT increased to a greater extent following inhibition of PKA and CaMKII phosphorylation in the OVx group compared with sham, both in the presence (by 69%, p < 0.0001) and absence (by 162%, p < 0.0001) of ISO respectively. CaT decay time significantly increased (by 21%, p < 0.01) in the sham group following inhibition of PKA and CaMKII together, whilst decay times in the OVx group remained unchanged in the presence and absence of ISO. At higher pacing rates, time to peak of the CaT decreased significantly (by 48%, p < 0.01) in the OVx group but not sham with inhibition of phosphorylation. Conclusion Our findings suggest ovariectomy alters intracellular calcium regulation and some of these effects appear to be mediated by alterations in phosphorylation of calcium handling proteins and/or changes to sites of phosphorylation.

Intracellular tetanic calcium signals are reduced in fatigue of whole skeletal muscle

1993 ◽  
Vol 264 (3) ◽  
pp. C577-C582 ◽  
Author(s):  
A. J. Baker ◽  
M. C. Longuemare ◽  
R. Brandes ◽  
M. W. Weiner
Keyword(s):  
Skeletal Muscle ◽  
Intracellular Calcium ◽  
Calcium Handling ◽  
Tetanic Stimulation ◽  
Muscle Contractility ◽  
Calcium Signals ◽  
Tetanic Force ◽  
Force Relaxation ◽  
Calcium Removal ◽  
Whole Muscle

Force and intracellular calcium signals were monitored in whole bullfrog semitendinosus muscles during fatigue produced by intermittent tetanic stimulation. Intracellular calcium signals were monitored using the fluorescent calcium-sensitive indicator indo-1 from the ratio of fluorescence intensities (R) at 400 and 470 nm. Fatiguing stimulation caused 1) proportional decreases of tetanic force and R, suggesting a component of the decreased force during fatigue of whole muscle may be due to insufficient calcium to activate contraction; 2) a progressive slowing of the relaxation of both force and R, suggesting slowed force relaxation may be mediated by slowed calcium removal from the myoplasm; 3) an increase of resting level R, suggesting impaired calcium removal from, or increased leakage to the cytosol; 4) prolongation of the twitch contraction, which was paralleled by changes in R. These findings are consistent with previous single fiber studies and suggest that changes in whole muscle contractility with fatigue may be partially mediated by changes in calcium handling by the cell.

scholarly journals Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

2020 ◽  
Vol 318 (1) ◽  
pp. L112-L124 ◽  
Author(s):  
Sangeeta Bhallamudi ◽  
Jennifer Connell ◽  
Christina M Pabelick ◽  
Y. S. Prakash ◽  
Venkatachalem Sathish
Keyword(s):  
Smooth Muscle ◽  
Estrogen Receptors ◽  
Intracellular Calcium ◽  
Airway Smooth Muscle ◽  
Airway Remodeling ◽  
Clinical Findings ◽  
Calcium Handling ◽  
Airway Smooth Muscle Cells ◽  
Adult Women ◽  
Channel Inhibition

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca2+]i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca2+]i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca2+]i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca2+] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca2+]i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca2+]i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca2+ sequestration by sarcoplasmic reticulum. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca2+]i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Cytosolic free Calcium and Intracellular Calcium Stores in Neutrophils from Hypertensive Subjects

1985 ◽  
Vol 69 (2) ◽  
pp. 227-230 ◽  
Author(s):  
P. Daniel Lew ◽  
Laurent Favre ◽  
Francis A. Waldvogel ◽  
Michel B. Vallotton
Keyword(s):  
Essential Hypertension ◽  
Intracellular Calcium ◽  
Calcium Ionophore ◽  
Calcium Handling ◽  
Free Calcium ◽  
Calcium Stores ◽  
Cytosolic Free Calcium ◽  
Intact Cells ◽  
Intracellular Calcium Stores ◽  
Calcium Indicator

1. Alterations in intracellular calcium have been implicated in the pathogenesis of essential hypertension. To see whether this is a generalized phenomenon we assessed cytosolic free calcium and intracellular calcium stores in neutrophils from normo- and hyper-tensive subjects, by trapping the fluorescent calcium indicator quin2 in intact cells. 2. Ten patients with untreated essential hypertension were compared with 10 age- and sex-matched normotensive subjects. The levels of cytosolic free calcium and intracellular calcium stores releasable by the calcium ionophore ionomycin did not differ. No significant relationship was found between blood pressure and the calcium parameters in all 20 subjects studied. 3. The results indicate that essential hypertension is not associated with a membrane defect in calcium handling of all human cell systems, leading to generalized increases in resting values of cytosolic free calcium. 4. Neutrophils do not appear to be a good model for intracellular calcium handling in vascular smooth muscle.

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