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 was simulated by centrifugation of cells into a pellet, and cell viability was determined by hypotonic trypan blue solution. Preconditioning was produced by brief exposures to either glucose-free solution or metabolic inhibition. Freshly isolated rabbit ventricular myocytes were studied to confirm that preconditioning occurs in this model. We then compared these results to those in several cultured cell lines, including HEK 293 cells derived from human embryonic kidney, HIT-T15 cells from Syrian hamster pancreatic islets, and C₂C₁₂ cells from mouse skeletal muscle. In the latter cell line, we also determined whether differentiation alters preconditioning. Preconditioning protected rabbit ventricular 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 myoblasts either. Interestingly, after C₂C₁₂ myoblasts had differentiated into myotubes (induced by exposing the cells to low-serum medium), they could then be protected by preconditioning (46.3±3.6% in the control group vs 26.0±2.7% in the preconditioned group after 60 min and 67.4±3.6% in the control group vs 46.0±4.6% in the preconditioned group after 120 min ischemia; p<0.05). In conclusion, protection from preconditioning is cell-type specific. The presence of endogenous K_ATP channels (which are plentiful in HIT-T15 cells) is insufficient to enable preconditioning of the cell. Among the various cell types studied, only differentiated muscle cells (rabbit ventricular myocytes and C₂C₁₂ myotubes) exhibited preconditioning.