Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC248
Elevated extracellular glucose markedly attenuates ischaemic preconditioning in cardiac ventricular myocytes
M. W. Sims1, I. B. Squire1, R. D. Rainbow1
1. Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom.
Elevation of blood glucose is associated with worsening of outcome for patients after acute myocardial infarction(1). Hyperglycaemia has been implicated as causative in a number of deleterious vascular complications and has recently been shown by us, and others, to affect cardiac tissue; in particular being pro-arrhythmic and to attenuate the protective effect of prodromal angina. In this study we have investigated the effects of elevations of extracellular glucose on the protection to cardiomyocytes afforded by ischaemic preconditioning. Ventricular myocytes were enzymatically isolated from excised hearts from adult male Wistar rats (animals were sacrificed in accordance with Home Office regulations). Excised hearts were ischaemically preconditioned (IPC) on a Langendorff system by interrupting perfusion 3 times for 5 minutes with 5 minutes of reperfusion between each stop(2). Cells were then isolated after the 3rd reperfusion. Cardioprotection was assessed by contractile recovery after a metabolic inhibition/reperfusion protocol mimicking ischaemia and reperfusion (I/R). Briefly, cells were perfused with 5 mM glucose containing normal Tyrode solution (NT) at 32±2°C and paced to contract at 1 Hz with electric field stimulation. This was followed by 7 minutes of substrate-free metabolic inhibition Tyrode (SFT) containing 2 mM cyanide and 1 mM iodoacetic acid. Finally the cells were reperfused with NT and contractile recovery was assessed at 10 minutes. In control cells 32±4% (n=112) of cells recovered their contractile function which increased to 88±3% (n=93) after IPC (P<0.001). Increasing extracellular glucose concentration markedly reduced the protection afforded by IPC, (10mM, 76±5% (n=74), 15mM, 70±4% (n=118) and 20mM, 56±5% (n=89)). In 20mM glucose 59±5% of control cells (i.e. those not subjected to IPC) recovered their contractile function suggesting that high glucose had abolished the additional protection afforded by IPC. These data suggest that hyperglycaemia abolishes certain mechanisms of cardioprotection in ventricular myocytes and that this is inversely proportional to the extracellular glucose concentration between 5-20mM. Previous data from our laboratory demonstrate that phorbol ester induced PKC-mediated cardioprotection (3) is markedly attenuated by elevated extracellular glucose. Such attenuation of cardioprotection is of clinical importance in defining the regulation of glycaemia in patients presenting with myocardial infarction. Increased understanding of the mechanisms by which cardioprotection occurs, and by which this is attenuated by extracellular hyperglycaemia, may lead to the development of clinically effective cardioprotective protocols for application in practice.
Where applicable, experiments conform with Society ethical requirements