LPCES对慢性低压缺氧兔颏舌肌肌球蛋白重链和SR Ca^(2+)摄取-释放动力学的影响

Electrical stimulation at lower physiological frequency induces myosin heavy chain isoform transformation and improves sarcoplasmic reticulum Ca^(2+) uptake/release in genioglossus of rabbits exposed to chronic hypoxia

目的研究超低频复合生理频率慢性电刺激(lower physiological frequency chronic electrical stimulation,LPCES)对慢性低压缺氧兔颏舌肌肌球蛋白重链(myosin heavy chain,MHC)亚型表达和肌浆网(sarcoplasmic reticulum,SR)Ca2+摄取-释放动力学的影响。方法成年日本大白兔24只,按随机数字表法分为4组(n=6):A:正常对照组,B:慢性低压缺氧组,C:2.5 Hz电刺激组,D:(2.5+40)Hz电刺激组。B、C、D组兔在构建慢性低压缺氧模型后,给予C、D 2组慢性电刺激,刺激频率分别为超低频2.5 Hz和超低频复合生理频率(2.5+40)Hz。采用Western blot分析4组兔颏舌肌MHC亚型表达变化,采用荧光光度测定法测定SR Ca2+摄取-释放动力学。结果①同正常对照组[(72.16±2.98)%]比较,慢性低压缺氧组[(80.45±1.26)%]兔颏舌肌MHCⅡa亚型比例明显增加(P<0.05),MHCⅠ亚型比例明显减少[(10.86±1.26)%vs(18.61±3.19)%,P<0.05],SR Ca2+摄取-释放速率明显下降,摄取-释放量也明显减少(P<0.05)。②同慢性低压缺氧组比较,慢性电刺激后各组兔MHCⅡa和MHCⅠ亚型比例明显增加(P<0.05),MHCⅡb亚型比例明显减少(P<0.05),(2.5+40)Hz电刺激组较2.5 Hz电刺激组更为显著(P<0.05);SR Ca2+摄取-释放速率加快,摄取-释放量增加(P<0.05),(2.5+40)Hz电刺激组较2.5 Hz电刺激组更为明显(P<0.05)。同2.5 Hz电刺激组比较,(2.5+40)Hz电刺激组MHCⅡa和MHCⅠ亚型比例差异无统计学意义(P>0.05)。结论慢性电刺激后慢性低压缺氧兔颏舌肌MHC呈现Ⅱb型向Ⅱa型和Ⅰ型的转变,SR Ca2+摄取-释放功能增强,其中超低频复合生理频率组变化更加明显。

Objective To identify the effect of chronic electrical stimulation at a lower physiological frequency on the expressions of myosin heavy chain（MHC） isoforms and kinetics of sarcoplasmic reticulum（SR） Ca2＋ uptake/release in the genioglossus of rabbits exposed to chronic hypoxia.Methods Twenty-four adult rabbits were randomized into control group（A）,chronic hypoxia group（B）,2.5 Hz electrical stimulation group（C） and（2.5＋40） Hz electrical stimulation group（low frequency plus physical frequency,D）.After the rabbits from group B,C and D had been fed with free access to food and water in a hypoxia cabin（simulating 5 000 m altitude） in 10 h a day for 4 weeks,the rabbits in group C and D received electrical stimulation in their genioglossus at a frequency of 2.5 Hz and（2.5＋40） Hz respectively in 10 h per day for 14 d,while those in group B received no electrical stimulation.Expressions of MHC isoforms in the genioglossus of rabbits in 4 groups were detected by Western blotting,and Fura-2 fluorophotometry was used to assay the kinetics changes of SR Ca2＋ uptake-release.Results The expression level of MHCⅡa was significantly higher while that of MHCⅠ was significantly lower in group B than that in group A（P0.05）.Meanwhile,the genioglossus SR Ca2＋ uptake/release velocity in group B was significantly decreased compared with that in group A（P0.05）.The expression levels of MHCⅡa and MHCⅠ in group C and D after electrical stimulation were significantly higher,while those of MHCⅡb,especially in group D,were significantly lower than those in group B（P0.05）.The genioglossus SR Ca2＋ uptake/release velocity in group C and D,especially in group D,was significantly increased compared with that in group B（P0.05）.No significant difference was found in expression levels of MHCⅡa and MHCⅠ between group C and D after electrical stimulation（P0.05）.Conclusion MHCⅡb in the genioglossus of rabbits with chronic hypoxia is transformed to MHCⅡa and MHCⅠ after electrical stimulation,and SR Ca2＋ uptake/release velocity is increased,especially at a lower physiological frequency of（2.5＋40） Hz.