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Regulation of Ca2+ signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes.

ABSTRACT: Ischemic heart disease is an arrhythmogenic condition, accompanied by hypoxia, acidosis, and impaired Ca2+ signaling. Here we report on effects of acute hypoxia and acidification in rat neonatal cardiomyocytes cultures. RESULTS:Two populations of neonatal cardiomyocyte were identified based on inactivation kinetics of L-type ICa: rapidly-inactivating ICa (?~20ms) myocytes (prevalent in 3-4-day cultures), and slow-inactivating ICa (??40ms) myocytes (dominant in 7-day cultures). Acute hypoxia (pO2<5mmHg for 50-100s) suppressed ICa reversibly in both cell-types to different extent and with different kinetics. This disparity disappeared when Ba2+ was the channel charge carrier, or when the intracellular Ca2+ buffering capacity was increased by dialysis of high concentrations of EGTA and BAPTA, suggesting critical role for calcium-dependent inactivation. Suppressive effect of acute acidosis on ICa (~40%, pH6.7), on the other hand, was not cell-type dependent. Isoproterenol enhanced ICa in both cell-types, but protected only against suppressive effects of acidosis and not hypoxia. Hypoxia and acidosis suppressed global Ca2+ transients by ~20%, but suppression was larger, ~35%, at the RyR2 microdomains, using GCaMP6-FKBP targeted probe. Hypoxia and acidosis also suppressed mitochondrial Ca2+ uptake by 40% and 10%, respectively, using mitochondrial targeted Ca2+ biosensor (mito-GCaMP6). CONCLUSION:Our studies suggest that acute hypoxia suppresses ICa in rapidly inactivating cell population by a mechanism involving Ca2+-dependent inactivation, while compromised mitochondrial Ca2+ uptake seems also to contribute to ICa suppression in slowly inactivating cell population. Proximity of cellular Ca2+ pools to sarcolemmal Ca2+ channels may contribute to the variability of inactivation kinetics of ICa in the two cell populations, while acidosis suppression of ICa appears mediated by proton-induced block of the calcium channel.

SUBMITTER: Fernandez-Morales JC

PROVIDER: S-EPMC5801211 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Regulation of Ca2+ signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes.

Fernández-Morales José-Carlos JC Morad Martin M

Journal of molecular and cellular cardiology 20171012

Ischemic heart disease is an arrhythmogenic condition, accompanied by hypoxia, acidosis, and impaired Ca2+ signaling. Here we report on effects of acute hypoxia and acidification in rat neonatal cardiomyocytes cultures.<h4>Results</h4>Two populations of neonatal cardiomyocyte were identified based on inactivation kinetics of L-type ICa: rapidly-inactivating ICa (τ~20ms) myocytes (prevalent in 3-4-day cultures), and slow-inactivating ICa (τ≥40ms) myocyt ...[more]

PMID: 29032102

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Project description:Recent evidence has shown that nanoparticles that have been used to improve or create new functional properties for common products may pose potential risks to human health. Silicon dioxide (SiO2) has emerged as a promising therapy vector for the heart. However, its potential toxicity and mechanisms of damage remain poorly understood. This study provides the first exploration of SiO2-induced toxicity in cultured cardiomyocytes exposed to 7- or 670-nm SiO2 particles. We evaluated the mechanism of cell death in isolated adult cardiomyocytes exposed to 24-h incubation. The SiO2 cell membrane association and internalization were analyzed. SiO2 showed a dose-dependent cytotoxic effect with a half-maximal inhibitory concentration for the 7 nm (99.5 ± 12.4 µg/ml) and 670 nm (>1,500 µg/ml) particles, which indicates size-dependent toxicity. We evaluated cardiomyocyte shortening and intracellular Ca2+ handling, which showed impaired contractility and intracellular Ca2+ transient amplitude during β-adrenergic stimulation in SiO2 treatment. The time to 50% Ca2+ decay increased 39%, and the Ca2+ spark frequency and amplitude decreased by 35 and 21%, respectively, which suggest a reduction in sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity. Moreover, SiO2 treatment depolarized the mitochondrial membrane potential and decreased ATP production by 55%. Notable glutathione depletion and H2O2 generation were also observed. These data indicate that SiO2 increases oxidative stress, which leads to mitochondrial dysfunction and low energy status; these underlie reduced SERCA activity, shortened Ca2+ release, and reduced cell shortening. This mechanism of SiO2 cardiotoxicity potentially plays an important role in the pathophysiology mechanism of heart failure, arrhythmias, and sudden death.NEW & NOTEWORTHY Silica particles are used as novel nanotechnology-based vehicles for diagnostics and therapeutics for the heart. However, their potential hazardous effects remain unknown. Here, the cardiotoxicity of silica nanoparticles in rat myocytes has been described for the first time, showing an impairment of mitochondrial function that interfered directly with Ca2+ handling.

Project description:BackgroundCa2+ signals in smooth muscle cells (SMCs) contribute to vascular resistance and control blood pressure. Increased vascular resistance in hypertension has been attributed to impaired SMC Ca2+ signaling mechanisms. In this regard, transient receptor potential vanilloid 4 (TRPV4SMC) ion channels are a crucial Ca2+ entry pathway in SMCs. However, their role in blood pressure regulation has not been identified.MethodsWe used SMC-specific TRPV4-/- (TRPV4SMC-/-) mice to assess the role of TRPV4SMC channels in blood pressure regulation. We determined the contribution of TRPV4SMC channels to the constrictor effect of α1 adrenergic receptor (α1AR) stimulation and elevated intraluminal pressure: 2 main physiologic stimuli that constrict resistance-sized arteries. The contribution of spatially separated TRPV4SMC channel subpopulations to elevated blood pressure in hypertension was evaluated in angiotensin II-infused mice and patients with hypertension.ResultsWe provide first evidence that TRPV4SMC channel activity elevates resting blood pressure in normal mice. α1AR stimulation activated TRPV4SMC channels through PKCα (protein kinase Cα) signaling, which contributed significantly to vasoconstriction and blood pressure elevation. Intraluminal pressure-induced TRPV4SMC channel activity opposed vasoconstriction through activation of Ca2+-sensitive K+ (BK) channels, indicating functionally opposite pools of TRPV4SMC channels. Superresolution imaging of SMCs revealed spatially separated α1AR:TRPV4 and TRPV4:BK nanodomains in SMCs. These data suggest that spatially separated α1AR-TRPV4SMC and intraluminal pressure-TRPV4SMC-BK channel signaling have opposite effects on blood pressure, with α1AR-TRPV4SMC signaling dominating under resting conditions. Furthermore, in patients with hypertension and a mouse model of hypertension, constrictor α1AR-PKCα-TRPV4 signaling was upregulated, whereas dilator pressure-TRPV4-BK channel signaling was disrupted, thereby increasing vasoconstriction and elevating blood pressure.ConclusionsOur data identify novel smooth muscle Ca2+-signaling nanodomains that regulate blood pressure and demonstrate their impairment in hypertension.

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Regulation of Ca2+ signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes.

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Regulation of Ca<sup>2+</sup> signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes.

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