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Simulated ischemia-induced preconditioning of isolated ventricular myocytes from young adult and aged Fischer-344 rat hearts

¹Department of Pharmacology and ²Division of Geriatric Medicine, Dalhousie University, Halifax, Nova Scotia, Canada

Submitted 24 April 2008 ; accepted in final form 12 June 2008

The impact of ischemic preconditioning (IPC) on contraction, Ca²⁺ homeostasis, and cell survival was compared in isolated ventricular myocytes from young adult (3 mo) and aged (24 mo) male Fischer-344 rats. Myocytes were field stimulated at 4 Hz (37°C). Contraction (edge detector) and intracellular Ca²⁺ (fura-2) were measured simultaneously. Viability was assessed with trypan blue. All cells were exposed to 30 min of simulated ischemia followed by reperfusion. Some cells were preconditioned by exposure to 5 min of simulated ischemia before prolonged ischemia. Pretreatment with IPC abolished postischemic contractile depression, inhibited diastolic contracture, and increased Ca²⁺ transient amplitudes in reperfusion in young adult and aged cells. IPC did not affect the modest rise in diastolic Ca²⁺ in ischemia in young adult myocytes. However, IPC abolished the marked rise in diastolic Ca²⁺ observed in ischemia and early reperfusion in aged myocytes. IPC also suppressed mechanical alternans in ischemia in aged cells, but younger myocytes showed little evidence of mechanical alternans whether or not cells were preconditioned. IPC markedly improved cell viability in reperfusion in young adult but not aged cells. These results suggest that IPC augments the recovery of contractile function in reperfusion by increasing Ca²⁺ transient amplitudes in ventricular myocytes from young adult and aged rats. IPC reduced diastolic Ca²⁺ accumulation in ischemia in aged myocytes, which may diminish the severity of mechanical alternans in aged cells. Nonetheless, the efficacy of IPC is compromised in aging, as IPC did not improve survival of aged myocytes exposed to ischemia and reperfusion.

cardioprotection; reperfusion; mechanical alternans; senescence

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