| Summary: | Ischemic preconditioning (IPC) and activation of ATP-sensitive potassium channels (K<sub>ATP</sub>) protect cardiac myocytes from ischemia reperfusion (IR) injury. We investigated the influence of IR injury, IPC and K<sub>ATP</sub> in isolated rat cardiac fibroblasts. Hearts were removed under isoflurane anesthesia. IR was simulated in vitro by application and removal of paraffin oil over pelleted cells. Ischemia (30, 60 and 120 min) followed by 60 min reperfusion resulted in significant differentiation of fibroblasts into myofibroblasts in culture (mean % fibroblasts ± SEM in IR vs. time control: 12 ± 1% vs. 63 ± 2%, 30 min ischemia; 15 ± 3% vs. 71 ± 4%, 60 min ischemia; 8 ± 1% vs. 55 ± 2%, 120 min ischemia). IPC (15 min ischemia, 30 min reperfusion) significantly attenuated IR-induced fibroblast differentiation (52 ± 3%) compared to 60 min IR. IPC was mimicked by opening K<sub>ATP</sub> with pinacidil (50 μM; 43 ± 6%) and by selectively opening mitochondrial K<sub>ATP</sub> (mK<sub>ATP</sub>) with diazoxide (100 μM; 53 ± 3%). Furthermore, IPC was attenuated by inhibiting K<sub>ATP</sub> with glibenclamide (10 μM; 23 ± 5%) and by selectively blocking mK<sub>ATP</sub> with 5-hydroxydecanoate (100 μM; 22 ± 9%). These results suggest that (a) IR injury evoked cardiac fibroblast to myofibroblast differentiation, (b) IPC attenuated IR-induced fibroblast differentiation, (c) K<sub>ATP</sub> were involved in IPC and (d) this protection involved selective activation of mK<sub>ATP</sub>.
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