Activation of ATP-sensitive potassium channels prevents the cleavage of cytosolic μ-calpain and abrogates the elevation of nuclear c-Fos and c-Jun expressions after hypoxic–ischemia in neonatal rat brain

Abstract

The purpose of this study was to determine whether activation of ATP-sensitive K + (K ATP) channels with diazoxide (DIZ) is able to prevent the cleavage of cytosolic μ-calpain and abrogate the elevation of nuclear c-Fos and c-Jun protein (c-Fos, c-Jun) expressions after hypoxic–ischemia (HI) in brain. The model of hypoxic–ischemic brain injury (HIBI) was made in the 7-day-old Sprague–Dawley (SD) rats by left carotid arterial ligation and hypoxia (8% oxygen). DIZ was injected into the left lateral ventricle (5 μl, 1 mg/ml) before or post-hypoxic–ischemia (HI) insults. Western blot and computer image processing were used to detect the integrated density of nuclear c-Fos and c-Jun at 4 h and cleavage of cytosolic μ-calpain at 24 h after HI insults from cerebral cortical and hippocampal samples. Compared with HI controls (c-Fos=30.37±7.39 from cortical samples, 58.61±3.64 from hippocampal samples; c-Jun=52.48±14.23 from cortical samples, 35.55±4.73 from hippocampal samples), there was a significant down-regulation of c-Fos and c-Jun expressions from cortical and hippocampal samples in rats treated with DIZ before (c-Fos=11.10±4.64 from cortical samples, 4.82±3.38 from hippocampal samples; c-Jun=19.01±5.29 from cortical samples, 35.55±4.73 from hippocampal samples) or post- (c-Fos=18.81±7.93 from cortical samples, 11.33±7.05 from hippocampal samples; c-Jun=24.64±10.01 from cortical samples, 19.75±3.47 from hippocampal samples) HI insults. Furthermore, the ratio of 76 kD/80 kD of μ-calpain was down-regulated from cortical and hippocampal samples in rats treated with DIZ before or post-HI insults, demonstrating a significant difference compared with that observed in HI controls. Finally, the increase in DNA fragments caused by the HI injury was decreased or eliminated by the treatment with DIZ. These data suggests that activation of K ATP channels by DIZ reduces the degree of μ-calpain proteolysis, and c-Fos and c-Jun expressions in immature brain may contribute to the neuroprotection of K ATP channel openers against HIBI.