HUMAN VENTRICULAR MYOCYTES IN-VITRO EXHIBIT BOTH EARLY AND DELAYED PRECONDITIONING RESPONSES TO SIMULATED ISCHEMIA

Myocardial tissue has been demonstrated to exhibit, in reponse to brie f periods of ischemia, both an immediate period of cytoprotection [i.e . early or ''first window'' preconditioning response (EPR)], and a lat er period of cytoprotection [i.e. delayed or ''second window'' precond itioning response (DPR)], when exposed to a subsequent prolonged hypox ic insult. EPR has been documented in vitro in isolated cardiac myocyt es, as well as in situ in intact hearts or trabeculae, for a number of vertebrate species, including humans. However, there are no reports t o date of DPR in human cardiac myocytes. To address this question, hum an ventricular myocytes (HVM) primary isolates were prepared from feta l ventricular muscle, grown to confluency, and studied in primary cult ure in serum-free medium (>90%) ventricular myocytes as determined by immunohistochemical analysis with an anti-myosin chain antibody). Usin g cell viability as determined by trypan blue exclusion, an EPR respon se could readily be detected following 15, 30, or 60 min of simulated ischemia (SI) in a hypoxic (<1 tau pO(2)) buffer containing 11 mmol/l 2-deoxyglucose, followed by a prolonged (c. 17 h) SI challenge. In add ition, 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 myocytes in vitro exhibit both ''first window '' and ''second window'' cytoprotective responses to subsequent, prolo nged ischemic stress. (C) 1998 Academic Press Limited.