Intracellular Zn2+ Increase in Cardiomyocytes Induces both Electrical and Mechanical Dysfunction in Heart via Endogenous Generation of Reactive Nitrogen Species

Abstract

Oxidants increase intracellular free Zn(2+) concentration ([Zn(2+)]i) in ventricular myocytes, which contributes to oxidant-induced alterations in excitation-contraction coupling (ECC). However, it is not clear whether increased [Zn(2+)]i in cardiomyocytes via increased reactive nitrogen species (RNS) has a role on heart function under pathological conditions, such as hyperglycemia. In this study, first we aimed to investigate the role of increased [Zn(2+)]i under in vitro condition in the development of both electrical and mechanical dysfunction of isolated papillary muscle strips from rat heart via exposed samples to a Zn(2+)-ionophore (Zn-pyrithione; 1 μM) for 20 min. Under simultaneous measurement of intracellular action potential and contractile activity in these preparations, Zn-pyrithione exposure caused marked prolongation in action potential repolarization phase and slowdown in both contraction and relaxation rates of twitch activity. Second, in order to demonstrate an association between increased [Zn(2+)]i and increased RNS, we monitored intracellular [Zn(2+)]i under an acute exposure of nitric oxide (NO) donor sodium nitroprusside, SNP, in freshly isolated quiescent cardiomyocytes loaded with FluoZin-3. Resting level of free Zn(2+) is significantly higher in cardiomyocytes under hyperglycemic condition compared to those of the controls, which seems to be associated with increased level of RNS production in hyperglycemic cardiomyocytes. Western blot analysis showed that Zn-pyrithione exposure induced a marked decrease in the activity of protein phosphatase 1 and 2A, member of macromolecular protein complex of cardiac ryanodine receptors, RyR2, besides significant increase in the phosphorylation level of extracellular signal-regulated kinase1/2 as a concentration-dependent manner. Overall, the present data demonstrated that there is a cross-relationship between increased RNS production and increased [Zn(2+)]i level in cardiomyocytes under pathological conditions such as hyperglycemia.

β3‐adrenergic receptor activation plays an important role in the depressed myocardial contractility via both elevated levels of cellular free Zn2+ and reactive nitrogen species

“…Most importantly, it has been clearly documented that ROS and RNS can cause a marked increase in cytosolic and mitochondrial Zn 2+ release under pathological condition in the heart (Lin et al, ) via a role with increased [Zn 2+ ] i as a second messenger of extracellular signals similar to [Ca 2+ ] i (Tuncay et al, ). Consequently, increased [Zn 2+ ] i could induce marked depression in the contractile activity of the heart (Tuncay & Turan, ). In this regard, the present findings clearly express the important mediator roles of β 3 ‐AR activation in ventricular cardiomyocytes together with the increased expression level of β 3 ‐AR in ventricular cardiomyocytes from MetS rats, in part, via a relation between elevated [Zn 2+ ] i and increased RNS.…”

Impact of Labile Zinc on Heart Function: From Physiology to Pathophysiology

“…It is now well accepted that a well-controlled Zn 2+ homeostasis via Zn 2+ regulatory mechanisms can control influx/efflux of zinc to prevent toxic zinc accumulation into cells, particularly endogenous labile Zn 2+ plays a significant role in cytotoxic events at single cell level, including cardiomyocytes [ 8 , 9 , 10 , 40 , 51 ]. As mentioned in many articles, Zn 2+ is essential for growth and development for both plants and mammalians.…”

“…Thus, the area of Zn 2+ -homeostasis seems to be emerging in cardiovascular disease. However, it has been demonstrated that labile Zn 2+ outside a narrow concentration range are toxic to a variety of cells [ 69 ], including cardiomyocytes [ 8 , 9 , 10 , 14 , 40 , 51 , 75 ].…”

“…As described in previous sections, labile Zn 2+ regulates the expression and activation of biological molecules such as ion channels, transcription factors, enzymes, adapters, and growth factors, along with their receptors in many cell types, including cardiomyocytes. Excess Zn 2+ can be detrimental to cells, particularly that of cardiomyocytes [ 8 , 9 , 10 , 14 ]. As an intracellular signal transducer in multiple cellular functions, it has been shown that intracellular labile Zn 2+ has an important role in ECC in cardiomyocytes by shaping Ca 2+ dynamics [ 9 , 51 , 98 ], while it acts as a neuromodulator in synaptic transmissions [ 122 , 123 ].…”

“…For this reason, even mild zinc-deficiency may impact numerous aspects of human health, including heart function [ 6 ]. Although Zn 2+ has traditionally been regarded as relatively nontoxic, recent studies have shown how high intracellular labile Zn 2+ level ([Zn 2+ ] i ) can be a potent killer of numerous cell types [ 7 ] including cardiomyocytes [ 8 , 9 , 10 ]. In cardiomyocytes, [Zn 2+ ] i is measured to be less than one nanomolar under physiological conditions being much less than the intracellular free Ca 2+ ([Ca 2+ ] i ) [ 8 , 11 ].…”