scholarly journals Two-variable nullcline analysis of ionic general equilibrium predicts calcium homeostasis in ventricular myocytes

2019 ◽  
Author(s):  
David Conesa ◽  
Blas Echebarria ◽  
Angelina Peñaranda ◽  
Inmaculada R. Cantalapiedra ◽  
Yohannes Shiferaw ◽  
...  
Keyword(s):  
Heart Failure ◽  
Gene Therapy ◽  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
General Equilibrium ◽  
Calcium Homeostasis ◽  
Ventricular Myocytes ◽  
Ionic Channels ◽  
Equilibrium Structure ◽  
Calcium Handling

AbstractVentricular contraction is roughly proportional to the amount of calcium released from the Sarcoplasmic Reticulum (SR) during systole. While it is rather straightforward to measure calcium levels and contractibility under different physiological condition, the complexity of calcium handling during systole and diastole has made the prediction of its release at steady state impossible. Here we approach the problem analyzing the evolution of intracellular and extracellular calcium fluxes during a single beat which is away from homeostatic balance. Using an in-silico subcellular model of rabbit ventricular myocyte, we show that the high dimensional nonlinear problem of finding the steady state can be reduced to a two-variable general equilibrium condition where pre-systolic calcium level in the cytosol and in the SR must fulfill simultaneously two different equalities. This renders calcium homeostasis as a problem that can be studied in terms of its equilibrium structure, leading to precise predictions of steady state from single-beat measurements. We show how changes in ionic channels modify the general equilibrium as shocks would do in general equilibrium macroeconomic models. This allows us to predict when an enhanced entrance of calcium in the cell reduces its contractibility and explain why SERCA gene therapy, a change in calcium handling to treat heart failure, might fail to improve contraction even when it successfully increases SERCA expression.Author summaryCardiomyocytes, upon voltage excitation, release calcium, which leads to cell contraction. However, under some pathological conditions, calcium handling is impaired. Recently, SERCA gene therapy, whose aim is to improve Ca2+ sequestration by the Sarcoplasmic Reticulum (SR), has failed to improve the prognosis of patients with Heart Failure. This, together with recent counterintuitive results in calcium handling, has highlighted the need for a framework to understand calcium homeostasis across species and pathologies. We show here that the proper framework is a general equilibrium approach of two independent variables. The development of this framework allows us to find a possible mechanism for the failure of SERCA gene therapy even when it manages to increase Ca SERCA expression.

Steady-state twitch Ca2+ fluxes and cytosolic Ca2+ buffering in rabbit ventricular myocytes

1996 ◽  
Vol 270 (1) ◽  
pp. C192-C199 ◽  
Author(s):  
L. M. Delbridge ◽  
J. W. Bassani ◽  
D. M. Bers
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Whole Cell ◽  
Rabbit Ventricular Myocytes ◽  
The Mean ◽  
State Contraction ◽  
Caffeine Contractures

Intracellular Ca2+ ([Ca2+]i) transients and transsarcolemmal Ca2+ currents were measured in indo 1-loaded isolated rabbit ventricular myocytes during whole cell voltage clamp to quantitate the components of cytosolic Ca2+ influx and to describe the dynamic aspects of cytosolic Ca2+ buffering during steady-state contraction (0.5 Hz, 22 degrees C). Sarcolemmal Ca2+ influx was directly measured from the integrated Ca2+ current (Ica) recorded during the clamp (158 +/- 10 attomoles; amol). Sarcoplasmic reticulum (SR) Ca2+ content was determined from the integrated electrogenic Na+/Ca2+ exchange current (Ix) induced during rapid application and sustained exposure of cells to caffeine to elicit the release of the SR Ca2+ load (1,208 +/- 170 amol). The mean steady-state SR Ca2+ load was calculated to be 87 +/- 13 microM (mumol/l nonmitochondrial cytosolic volume). Ca2+ influx via Ica represented approximately 14% of the stored SR Ca2+ and 23% of the total cytosolic Ca2+ flux during a twitch (47 +/- 6 microM). Comparison of electrophysiologically measured Ca2+ fluxes with Ca2+ transients yields apparent buffering values of 60 for caffeine contractures and 110 for twitches (delta Ca2+ total/delta Ca2+ free). This is consistent with the occurrence of "active" buffering of cytosolic Ca2+ by SR Ca2+ uptake during the twitch.

scholarly journals Role of Oxidative Stress in Heart Failure: Insights from Gene Transfer Studies

Biomedicines ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1645
Author(s):  
Bart De Geest ◽  
Mudit Mishra
Keyword(s):  
Oxidative Stress ◽  
Heart Failure ◽  
Gene Therapy ◽  
Steady State ◽  
Gene Transfer ◽  
Oxidative Modification ◽  
Heme Oxygenase 1 ◽  
Therapy Studies ◽  
Pathological Remodeling

Under physiological circumstances, there is an exquisite balance between reactive oxygen species (ROS) production and ROS degradation, resulting in low steady-state ROS levels. ROS participate in normal cellular function and in cellular homeostasis. Oxidative stress is the state of a transient or a persistent increase of steady-state ROS levels leading to disturbed signaling pathways and oxidative modification of cellular constituents. It is a key pathophysiological player in pathological hypertrophy, pathological remodeling, and the development and progression of heart failure. The heart is the metabolically most active organ and is characterized by the highest content of mitochondria of any tissue. Mitochondria are the main source of ROS in the myocardium. The causal role of oxidative stress in heart failure is highlighted by gene transfer studies of three primary antioxidant enzymes, thioredoxin, and heme oxygenase-1, and is further supported by gene therapy studies directed at correcting oxidative stress linked to metabolic risk factors. Moreover, gene transfer studies have demonstrated that redox-sensitive microRNAs constitute potential therapeutic targets for the treatment of heart failure. In conclusion, gene therapy studies have provided strong corroborative evidence for a key role of oxidative stress in pathological remodeling and in the development of heart failure.

scholarly journals Two-variable nullcline analysis of ionic general equilibrium predicts calcium homeostasis in ventricular myocytes

2020 ◽  
Vol 16 (6) ◽  
pp. e1007572
Author(s):  
David Conesa ◽  
Blas Echebarria ◽  
Angelina Peñaranda ◽  
Inmaculada R. Cantalapiedra ◽  
Yohannes Shiferaw ◽  
...  
Keyword(s):  
General Equilibrium ◽  
Calcium Homeostasis ◽  
Ventricular Myocytes

Calcium handling by sarcoplasmic reticulum of neonatal swine cardiac myocytes

1997 ◽  
Vol 273 (1) ◽  
pp. H192-H199
Author(s):  
C. M. Hohl ◽  
B. Livingston ◽  
J. Hensley ◽  
R. A. Altschuld
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Heart Function ◽  
Binding Capacity ◽  
Calcium Handling ◽  
Maximal Effect ◽  
Binding Studies ◽  
Human Infants ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Length Changes

In recent years, because of similarities to human infants, neonatal piglets have increasingly become the model of choice for studying neonatal heart function. However, the cardiac sarcoplasmic reticulum (SR) has not been thoroughly characterized in this species. Accordingly, Ca2+ pump kinetics, efflux channel characteristics, Ca2+ transients, and contractile movements were examined in isolated newborn piglet cardiac ventricular myocytes. Maximum uptake rate (Vmax) and concentration required to produce a half-maximal effect (K0.5) for oxalate-supported, ATP-dependent 45Ca2+ uptake by the SR of digitonin-lysed myocytes were 285 +/- 17 nmol 45Ca2+.min-1.mg-1 and 0.69 +/- 0.07 microM, respectively. In the absence of phospholamban phosphorylation, Vmax was reduced to 195 +/- 26 nmol 45Ca2+.min-1.mg-1 (P < 0.05 vs. control) and K0.5 increased to 1.28 +/- 0.13 microM (P < 0.05 vs. control). [3H]ryanodine binding studies yielded a maximum binding capacity of 181 +/- 12 fmol/mg and a dissociation constant of 1.7 +/- 0.2 nM. Raising extracellular Ca2+ (0.5-5 mM) increased peak amplitude and decreased the duration of electrically stimulated fura 2 Ca2+ transients and recordings of cell length changes. Both ryanodine and 2,5-di-tert-butylhydroquinone, an inhibitor of SR calcium adenosinetriphosphatase, completely abolished Ca2+ transients in piglet myocytes. These studies indicate that the SR has a significant role in excitation-contraction coupling in neonatal piglet myocytes.

Intracellular calcium handling in ventricular myocytes from mdx mice

2007 ◽  
Vol 292 (2) ◽  
pp. H846-H855 ◽  
Author(s):  
Iwan A. Williams ◽  
David G. Allen
Keyword(s):  
Heart Failure ◽  
Protein Expression ◽  
Transient Receptor Potential ◽  
Ventricular Myocytes ◽  
Clinical Symptoms ◽  
Disease Process ◽  
Calcium Handling ◽  
Mdx Mouse ◽  
Mdx Mice ◽  
Age Related

Duchenne muscular dystrophy (DMD) is a lethal degenerative disease of skeletal muscle, characterized by the absence of the cytoskeletal protein dystrophin. Some DMD patients show a dilated cardiomyopathy leading to heart failure. This study explores the possibility that dystrophin is involved in the regulation of a stretch-activated channel (SAC), which in the absence of dystrophin has increased activity and allows greater Ca2+ into cardiomyocytes. Because cardiac failure only appears late in the progression of DMD, we examined age-related effects in the mdx mouse, an animal model of DMD. Ca2+ measurements using a fluorescent Ca2+-sensitive dye fluo-4 were performed on single ventricular myocytes from mdx and wild-type mice. Immunoblotting and immunohistochemistry were performed on whole hearts to determine expression levels of key proteins involved in excitation-contraction coupling. Old mdx mice had raised resting intracellular Ca2+ concentration ([Ca2+]i). Isolated ventricular myocytes from young and old mdx mice displayed abnormal Ca2+ transients, increased protein expression of the ryanodine receptor, and decreased protein expression of serine-16-phosphorylated phospholamban. Caffeine-induced Ca2+ transients showed that the Na+/Ca2+ exchanger function was increased in old mdx mice. Two SAC inhibitors streptomycin and GsMTx-4 both reduced resting [Ca2+]i in old mdx mice, suggesting that SACs may be involved in the Ca2+-handling abnormalities in these animals. This finding was supported by immunoblotting data, which demonstrated that old mdx mice had increased protein expression of canonical transient receptor potential channel 1, a likely candidate protein for SACs. SACs may play a role in the pathogenesis of the heart failure associated with DMD. Early in the disease process and before the onset of clinical symptoms increased, SAC activity may underlie the abnormal Ca2+ handling in young mdx mice.

scholarly journals Tricyclic antidepressant amitriptyline alters sarcoplasmic reticulum calcium handling in ventricular myocytes

2008 ◽  
Vol 295 (5) ◽  
pp. H2008-H2016 ◽  
Author(s):  
Aleksey V. Zima ◽  
Jia Qin ◽  
Michael Fill ◽  
Lothar A. Blatter
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Tricyclic Antidepressant ◽  
Calcium Handling ◽  
Direct Stimulation ◽  
Open Probability ◽  
Open Time ◽  
Ca Uptake ◽  
Dose Dependent Fashion ◽  
High Concentrations

Tricyclic antidepressants such as amitriptyline (AMT) have been reported to have adverse side effects on cardiac performance. AMT effects on Ca handling in ventricular myocytes, however, are not well understood. Therefore, we investigated AMT action on sarcoplasmic reticulum (SR) Ca release in ventricular myocytes, ryanodine receptor (RyR) activity, and Ca uptake by SR microsomes. In permeabilized myocytes, AMT transiently increased free luminal Ca concentration ([Ca]) followed by marked depletion. AMT (10 μM) caused a rapid and a transient increase of Ca spark frequency, followed by a significant suppression of spark activity. The latter was associated with a decrease of Ca spark amplitude and SR Ca load to 87 and 60%, respectively. AMT (10 μM) completely abolished propagation of spontaneous Ca waves. Higher concentrations of AMT (0.1–1 mM) evoked SR Ca release reminiscent of the effect of caffeine (20 mM) and caused almost complete depletion of SR Ca content. Studies on single calsequestrin-free RyR channels revealed that AMT increased the mean open time and open probability ( Po) in a dose-dependent fashion (dissociation constant = 4.2 μM). High concentrations of AMT (>25 μM) evoked frequent long openings with Po reaching very high levels (>0.70). In studies with cardiac SR microsomes, AMT slowed the rate of ATP-dependent Ca uptake. We conclude that AMT affects SR Ca handling in ventricular myocytes by multiple mechanisms, including direct stimulation of RyRs and inhibition of SR Ca uptake. These effects could contribute to AMT cardiotoxicity.

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