Human Ventricular Myocytesin VitroExhibit both Early and Delayed Preconditioning Responses to Simulated Ischemia

Myocardial tissue has been demonstrated to exhibit, in reponse to brief periods of ischemia, both an immediate period of cytoprotection [i.e. early or ««first window»» preconditioning response (EPR)], and a later period of cytoprotection [i.e. delayed or ««second window»» preconditioning response (DPR)], when exposed to a subsequent prolonged hypoxic insult. EPR has been documentedin vitroin isolated cardiac myocytes, as well asin situin intact hearts or trabeculae, for a number of vertebrate species, including humans. However, there are no reports to date of DPR in human cardiac myocytes. To address this question, human ventricular myocytes (HVM) primary isolates were prepared from fetal ventricular muscle, grown to confluency, and studied in primary culture in serum-free medium (>90%) ventricular myocytes as determined by immunohistochemical analysis with an anti-myosin chain antibody). Using cell viability as determined by trypan blue exclusion, an EPR response could readily be detected following 15, 30, or 60 min of simulated ischemia (SI) in a hypoxic (<1upO2) buffer containing 11 mmol/l 2-deoxy-glucose, followed by a prolonged (c.17 h) SI challenge. In addition, HVM exposed to 60 min of SI, followed after 24 h by a period of SI, also exhibited a ««second window»» DPR (80±10% compared to 71±11% survival, in preconditioned and non-preconditioned cultures;P<0.05;n=18 independent experiments). Thus, in response to short periods of SI, human ventricular myocytesin vitroexhibit both ««first window»» and ««second window»» cytoprotective responses to subsequent, prolonged ischemic stress.