PKC-mediated toxicity of elevated glucose concentration on cardiomyocyte function

Abstract

While it is well established that mortality risk after myocardial infarction (MI) increases in proportion to blood glucose concentration at the time of admission, it is unclear whether there is a direct, causal relationship. We investigated potential mechanisms by which increased blood glucose may exert cardiotoxicity. Using a Wistar rat or guinea-pig isolated cardiomyocyte model, we investigated the effects on cardiomyocyte function and electrical stability of alterations in extracellular glucose concentration. Contractile function studies using electric field stimulation (EFS), patch-clamp recording, and Ca2+ imaging were used to determine the effects of increased extracellular glucose concentration on cardiomyocyte function. Increasing glucose from 5 to 20 mM caused prolongation of the action potential and increased both basal Ca2+ and variability of the Ca2+ transient amplitude. Elevated extracellular glucose concentration also attenuated the protection afforded by ischemic preconditioning (IPC), as assessed using a simulated ischemia and reperfusion model. Inhibition of PKCα and β, using Gö6976 or specific inhibitor peptides, attenuated the detrimental effects of glucose and restored the cardioprotected phenotype to IPC cells. Increased glucose concentration did not attenuate the cardioprotective role of PKCε, but rather activation of PKCα and β masked its beneficial effect. Elevated extracellular glucose concentration exerts acute cardiotoxicity mediated via PKCα and β. Inhibition of these PKC isoenzymes abolishes the cardiotoxic effects and restores IPC-mediated cardioprotection. These data support a direct link between hyperglycemia and adverse outcome after MI. Cardiac-specific PKCα and β inhibition may be of clinical benefit in this setting.

Distinct and complementary roles for α and β isoenzymes of PKC in mediating vasoconstrictor responses to acutely elevated glucose

“…In the present study, we have addressed this hypothesis by investigating the link between acute elevations in glucose concentration and changes in vascular function. We present data demonstrating for the first time that a glucose concentration‐dependent increase in vessel contraction is mediated by the DAG‐ and Ca 2+ ‐sensitive PKCα and PKCβ isoenzymes, as also recently shown in cardiomyocytes (Sims et al , ). This mechanism appears to be common to rat mesentery, porcine coronary and human internal mammary arterial tissues.…”

“…Acute elevations of extracellular glucose have also been shown to have deleterious effects on the electrical properties of isolated cardiomyocytes, causing a marked prolongation of action potential duration (Hreiche et al, 2009) and subsequent QT prolongation, which is suggested to be pro-arrhythmic (Marfella et al, 2001;Gordin et al, 2008). Our own recent findings suggest a similar DAG/Ca 2+ -PKC isoenzyme-dependent dysregulation of electrical signalling in cardiac tissue (Sims et al, 2014). The findings of the current study provide evidence for a common potential mechanism through which elevated glucose may exert direct deleterious effects on cardiovascular function with similar DAG/Ca 2+ -PKC isoenzyme-dependent mechanisms being evident in both heart and vasculature.…”

Intracellular Zinc Modulates Cardiac Ryanodine Receptor-mediated Calcium Release

“…The protocol for isolation of cardiomyocytes was as described previously ( 26 ). Briefly, the whole heart was rapidly excised and placed into cold, nominally Ca 2+ -free Tyrode's solution (NT).…”

Detachment of surface membrane invagination systems by cationic amphiphilic drugs

“…Normal physiological saline (NPS), used in all experiments on living megakaryocytes, consisted of 145 mM NaCl, 5 mM KCl, 1 mM MgCl 2 , 1 mM CaCl 2 , 10 mM HEPES, 10 mM glucose, pH 7.35 with NaOH. Ventricular myocytes were prepared using retrograde perfusion via a Langendorff cannula as described in detail elsewhere 69 . Briefly, the heart was rapidly excised, placed into cold Ca 2+ -free Tyrode’s solution (0CaTS; 5 mM KCl, 135 mM NaCl, 0.33 mM NaH 2 PO 4 , 5 mM Na Pyruvate, 10 mM HEPES, 15 mM mannitol, 5 mM glucose, 1 mM MgCl 2 ) and rapidly cannulated via the aorta.…”