| Ischemic preconditioning (IPC ), a phenomenon in which brief episodes of ischemia and reperfusion before a prolonged ischemic event limit myocardial injury, has been classified into two phases: an early phase and a delayed phase of cardioprotection. It would be beneficial to find novel antiischemic drugs and probe the mechanism of IPC if this powerful myocardial protection could be mimicked pharmacologically without the deleterious effects of preconditioning ischemia. Goq/n protein, an intermediary between the extracellular messenger binding with its receptor and intracellular effector, is a signal transduction protein which widely exists in tissues. The ATP-sensitive potassium channel ( KATP channel ) regulated by intracellular ATP, is an inward rectifier current potassium channel which widely exists on the myocardial sarcolemma and organellae . This channel has been suggested as a end-effector in the mechanism of ischemic preconditioning. Our previous research had demonstrated that pretreatment of rats with PGEi had cardioprotective effects, but the specific mechanism is not clear. We investigated the effect of Goq/11 signaling pathway and KATP channel on prostaglandin E1(PGEi) induced early preconditioning and delay preconditioning protection in rat hearts.Methods Two series of experiments were performed in Wistar rat hearts. The firstseries of experiment was used to investigate the effect of KATP channel on PGEi induced early preconditioning and delay preconditioning protection in rat hearts., all rats were subjected to 30 min of ischemia and 90 min reperfusion ( I/R ). (1)Myocardial ischemia/reperfusion( MI/R ) group rats, 2ml normal saline was injected(0.1ml-min~' ) 40 min before I/R; (2)PGEi early preconditioning protrection ( EPP ) group rats were injected 20 min PGE1 (1.25Mg-kg-1.min-1) 40 min before I/R; (3) PGEi delayed preconditioning protection ( DPP ) group rats were injected 20 min PGEi 23 h 20 min before I/R;(4)Glibenclamide ( Gli ) group rats were given glibenclamide ( 1mg.kg-1 ) 30 min before I/R; (5)Gli+EPP group rats were injected 20 min PGE1 40 min before I/R, and glibenclamide 30 min before I/R; (6)Gli+DPP group rats were injected 20 min PGE1 23 h 20min before I/R, and glibenclamide 30 min before I/R . Hemodynarnics, infarct size/area at risk ( IS/AAR ) of myocardium and scores of ventricular arrhythmia were measured. The expression of Gaq/n in sarcolemma was measured in the following groups by Western blot analysis in the second series: Sham operated control group ( Control group ), MI/R group, EPP group and DPP group. After removal of the atria and right ventricle , the frozen heart was sliced into 5-6 sections, and the slices were incubated in 1% triphenyltetrazolium chloride ( TTC ). The slices were immersed in 10% formalin overnight. The infarcted myocardium was dissected from the AAR under the illumination of a dissecting microscope. IS, AAR, and LV were determined by gravimetric analysis. The expression of Gaq/n in sarcolemma was measured by Western blot analysis.Results (1) Hemodynarnics Myocardical functional parameters, such as left ventricular systolic pressure, +dp/dt, and left ventricular end-diastolic pressure (LVEDP) were similar among the six groups at baseline ( P > 0.05 ), In the ischemic/reperfused period, LVEDP was significantly lower in the PGE1 pretreat groups as compared with the MI/R ( both, P < 0.01 ). The improvement of LVEDP induced by PGE1 was abolished by glibenclamide in Gli+EPP and Gli+DPP ( P > 0.05, compared with MI/R). Glibenclamide itself had no significant effect on LVEDP. (2) Infarct size The area atrisk ( % LV ) was not different between groups[(37.9±2.0)%, (39.3 + 2.2)%, (38.5 ± 2.3)%, (39.9 ± 2.3)%, (38.1 ±2.3)% vs (38.6 ±2.3)%, P > 0.05]. Infarct size was significantly reduced in the PGEi pretreat groups compared with MI/R [(12.3± 0.8)%, (11.7 ± 0.8)% vs (21.8± 1.5)%, P < 0.01 ], and this effect was significantly attenuated by glibenclamide in Gli+EPP and Gli+DPP compared with MI/R [(20.8 + 1.1)%, (21.4± 1.1)% vs (21.8 ± 1... |
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