CELL-TYPE SPECIFICITY OF PRECONDITIONING IN AN IN-VITRO MODEL

We investigated whether preconditioning could protect several cultured cell lines, to determine whether the protection is specific for cells derived from different myogenic and non-myogenic sources. Ischemia wa s simulated by centrifugation of cells into a pellet, and cell viabili ty was determined by hypotonic trypan blue solution. Preconditioning w as produced by brief exposures to either glucose-free solution or meta bolic inhibition. Freshly isolated rabbit ventricular myocytes were st udied to confirm that preconditioning occurs in this model. We then co mpared these results to those in several cultured cell lines, includin g HEK 293 cells derived from human embryonic kidney, HIT-T15 cells fro m Syrian hamster pancreatic islets, and C2C12 cells from mouse skeleta l muscle. In the latter cell line, we also determined whether differen tiation alters preconditioning. Preconditioning protected rabbit ventr icular myocytes: the percentage of dead cells was decreased from 36.8 +/- 4.7 % in the control group to 23.0 +/- 5.2 % in the preconditioned group after 60 min and from 50.7 +/- 2.1 % in the control group to 25 .5 +/- 4.5 % in the preconditioned group after 120 min ischemia (p < 0 .02). In contrast, there was no protection from preconditioning in HEK 293 cells or HIT-T15 cells. Preconditioning did not protect C2C12 myo blasts either. Interestingly, after C2C12 myoblasts had differentiated into myotubes (induced by exposing the cells to low-serum medium), th ey could then be protected by preconditioning (46.3 +/- 3.6 % in the c ontrol group vs 26.0 +/- 2.7 % in the preconditioned group after 60 mi n and 67.4 +/- 3.6 % in the control group vs 46.0 +/- 4.6 % in the pre conditioned group after 120 min ischemia; p < 0.05). In conclusion, pr otection from preconditioning is cell-type specific. The presence of e ndogenous K-ATP channels (which are plentiful in HIT-T15 cells) is ins ufficient to enable preconditioning of the cell. Among the various cel l types studied, only differentiated muscle cells (rabbit ventricular myocytes and C2C12 myotubes) exhibited preconditioning.