Amplitude Of Systolic Ca Research Articles

Effects of Advanced Glycation End Products on Calcium Handling in Cardiomyocytes

Background and Aims: Advanced glycation end products (AGEs) accumulate in diabetes and the engagement of receptor for AGE (RAGE) by AGEs contributes to the pathogenesis of diabetic cardiomyopathy. This study aims to investigate the effects of AGE/RAGE on ryanodine receptor (RyR) activity and Ca²⁺ handling in cardiomyocytes to elucidate the possible mechanism underlying cardiac dysfunction in diabetic cardiomypathy. Methods and Results: Confocal imaging Ca²⁺ spark, the elementary Ca²⁺ release event reflecting RyR activity in intact cell, as well as SR Ca²⁺ content and systolic Ca²⁺ transient were performed in cultured neonatal rat ventricular myocytes. The results show that 50 mg/ml AGE increased the frequency of Ca²⁺ sparks by 160%, while 150 mg/ml AGE increased it by 53%. AGE decreased the amplitude, width and duration of Ca²⁺ sparks. Blocking RAGE with anti-RAGE IgG completely abolished the alteration of Ca²⁺ sparks. The SR Ca²⁺ content indicated by the amplitude (ΔF/F0) of 20 m<smlcap>M</smlcap> caffeine-elicited Ca²⁺ transient was significantly decreased by 150 mg/ml AGE. In parallel, the amplitude of systolic Ca²⁺ transient evoked by 1 Hz-field stimulation was remarkably decreased by 150 mg/ml AGE. The anti-RAGE antibody completely restored the impaired SR load and systolic Ca²⁺ transient. Conclusion: AGE/RAGE signal enhanced Ca²⁺ spark-mediated SR Ca²⁺ leak, causing partial depletion of SR Ca²⁺ content and consequently decreasing systolic Ca²⁺ transient, which may contribute to contractile dysfunction in diabetic cardiomyopathy.

Polydatin attenuates cardiac hypertrophy through modulation of cardiac Ca2+ handling and calcineurin-NFAT signaling pathway.

Polydatin (PD), a resveratrol glucoside extracted from the perennial herbage Polygonum cuspidatum, has been suggested to have wide cardioprotective effects. This study aimed to explore the direct antihypertrophic role of PD in cultured neonatal rat ventricular myocytes (NRVMs) and its therapeutic effects against pressure overload (PO)-induced hypertrophic remodeling and heart failure. Furthermore, we investigated the mechanisms underlying the actions of PD. Treatment of NRVMs with phenylephrine for 72 h induced myocyte hypertrophy, where the cell surface area and protein levels of atrial natriuretic peptide and β-myosin heavy chain (β-MHC) were significantly increased. The amplitude of systolic Ca(2+) transient was increased, and sarcoplasmic reticulum Ca(2+) recycling was prolonged. Concomitantly, calcineurin activity was increased and NFAT protein was imported into the nucleus. PD treatment restored Ca(2+) handling and inhibited calcineurin-NFAT signaling, thus attenuating the hypertrophic remodeling in NRVMs. PO-induced cardiac hypertrophy was produced by transverse aortic constriction (TAC) in C57BL/6 mice, where the left ventricular posterior wall thickness and heart-to-body weight ratio were significantly increased. The cardiac function was increased at 5 wk of TAC, but significantly decreased at 13 wk of TAC. The amplitude of Ca(2+) transient and calcineurin activity were increased at 5 wk of TAC. PD treatment largely abolished TAC-induced hypertrophic remodeling by inhibiting the Ca(2+)-calcineurin pathway. Surprisingly, PD did not inhibit myocyte contractility despite that the amplitude of Ca(2+) transient was decreased. The cardiac function remained intact at 13 wk of TAC. In conclusion, PD is beneficial against PO-induced cardiac hypertrophy and heart failure largely through inhibiting the Ca(2+)-calcineurin pathway without compromising cardiac contractility.

Simultaneous Measurement of Cytoplasmic and SR Calcium during Modulation of Ryanodine Receptor Open Probability in Dog Ventricular Myocytes

We have previously found that, in rat ventricular myocytes, increasing ryanodine receptor open probability using low concentrations of caffeine had no maintained effect on the amplitude of systolic Ca. On application of caffeine, following an initial increase, systolic Ca returned to control levels in around 20 s and it was argued that this was due to a concurrent decrease in SR Ca. In the present study, we sought to obtain direct evidence for the involvement of a decrease of SR Ca in this transient response.SR Ca was measured directly with Mag-Fura-2. Application of 0.5 mM caffeine initially caused a 197 % increase in the amplitude of systolic Ca. This was associated with a 874 % increase in the amplitude of SR Ca loss and a 328 and 178 % increase in the rate of systolic cytoplasmic Ca removal and SR Ca replenishment respectively. In sustained caffeine exposure, all these parameters returned to levels comparable to control, typically within 1 - 2 beats. During caffeine exposure, SR Ca content rapidly decreased within 1 - 2 beats to a new steady state level. All measured parameters recovered to control levels on removal of caffeine.These data show, on RyR potentiation, following the initial increase, the secondary decrease of systolic Ca is due to a decrease in SR Ca.

Redox modification of ryanodine receptors underlies calcium alternans in a canine model of sudden cardiac death

Although cardiac alternans is a known predictor of lethal arrhythmias, its underlying causes remain largely undefined in disease settings. The potential role of, and mechanisms responsible for, beat-to-beat alternations in the amplitude of systolic Ca(2+) transients (Ca(2+) alternans) was investigated in a canine post-myocardial infarction (MI) model of sudden cardiac death (SCD). Post-MI dogs had preserved left ventricular (LV) function and susceptibility to ventricular fibrillation (VF) during exercise. LV wedge preparations from VF dogs were more susceptible to action potential (AP) alternans and the frequency-dependence of Ca(2+) alternans was shifted towards slower rates in myocytes isolated from VF dogs relative to controls. In both groups of cells, cytosolic Ca(2+) transients ([Ca(2+)](c)) alternated in phase with changes in diastolic Ca(2+) in sarcoplasmic reticulum ([Ca(2+)](SR)), but the dependence of [Ca(2+)](c) amplitude on [Ca(2+)](SR) was steeper in VF cells. Abnormal ryanodine receptor (RyR) function in VF cells was indicated by increased fractional Ca(2+) release for a given amplitude of Ca(2+) current and elevated diastolic RyR-mediated SR Ca(2+) leak. SR Ca(2+) uptake activity did not differ between VF and control cells. VF myocytes had an increased rate of reactive oxygen species production and increased RyR oxidation. Treatment of VF myocytes with reducing agents normalized parameters of Ca(2+) handling and shifted the threshold of Ca(2+) alternans to higher frequencies. Redox modulation of RyRs promotes generation of Ca(2+) alternans by enhancing the steepness of the Ca(2+) release-load relationship and thereby providing a substrate for post-MI arrhythmias.