Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC138
Ischaemic preconditioning and remote ischaemic preconditioning modulate pre-ischaemic Ca2+ homeostasis in rat ventricular myocytes
H. E. Turrell1, N. J. Samani1, G. C. Rodrigo1
1. Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom.
Ischaemic preconditioning (IPC), where the heart is subjected to one or more short periods of ischaemia prior to a longer period of index ischaemia, provides significant cardioprotection (1). More recently it has been demonstrated that preconditioning of organs or tissues remote from the heart can result in a similar cardioprotective effect known as remote ischaemic preconditioning (rIPC). Maintenance of Ca2+ homeostasis during ischaemia and reperfusion is important both for protection against reperfusion injury (2) and for the re-establishment of function post MI. We have therefore examined how IPC affects Ca2+ homeostasis in rat ventricular myocytes from hearts subject to IPC and in control myocytes following rIPC. Isolated hearts were subject to IPC consisting of 3 cycles of 5 min global ischaemia and reperfusion. Ventricular myocytes were isolated from control and IPC hearts by enzymatic dissociation (3). The first 3ml of perfusate eluted from the heart following each period of preconditioning ischaemia were retained for use in rIPC experiments. rIPC was achieved by treating cells with this perfusate for 10 minutes followed by a 5 minute washout period. Measurements of [Ca2+]i were made using Fura-2. L-type Ca2+ current was measured using whole-cell patch clamp. Values are mean±SEM compared by ANOVA followed by Tukey’s post-test (n= hearts, cells). IPC increased systolic [Ca2+]i from 486±17nM (n=10, 70) in control cells to 547±30nM (n=6, 28) in IPC cells although this was not significant, while rIPC reduced systolic [Ca2+]i to 413±21nM (n=4, 35, P<0.05). SR Ca2+ content measured by application of 20mM caffeine was unaltered following IPC (430±16nM (n=10, 46) in control cells, 386±21nM (n=6, 24) in IPC cells, 409±34nM (n=4, 18) in rIPC cells). The time constant for the decay of the Ca2+ transient (τ) was faster in IPC cells (119±4ms, n=6, 27) than in control cells (132±3ms, n=10, 71, P<0.05), suggesting that the rate of Ca2+ uptake into the SR was increased. The decay of the Ca2+ transient was also faster following rIPC (111 ±2ms, n=4, 35, P<0.01), mirroring the changes observed for IPC. The time constant for the decay of the caffeine-evoked Ca2+ release (τ) was faster in both IPC cells (2.5±0.1s, n=6, 16, P<0.01) and rIPC cells (2.9±0.2s, n=4, 16, P<0.01) than in control cells (3.7±0.3s n=10, 28), indicating that the activity of NCX is increased by IPC and rIPC. The L-type Ca2+ current at 0mV was significantly increased from -9.1±0.7pA/pF (n=2, 10) in control cells to -14.6±1.3pA/pF (n=2, 10) following IPC (P<0.01). Our data shows that IPC and rIPC modulate pre-ischaemic Ca2+ handling in ventricular myocytes and this may be involved in their protective effect. However, significant differences are apparent between myocytes isolated following whole heart IPC and rIPC of naïve myocytes.
Where applicable, experiments conform with Society ethical requirements