Effects Of Cigarette Smoke Exposure On Contractility And Myosin Heavy Chain Protein And Gene Expression In Genioglossus Of Rats

Objective: To investigate the effects of cigarette smoke exposure on the contractile function of genioglossus in rat and the association with myosin heavy chain(MHC)isoforms.Methods: Thirty 8-week-old male Sprague-Dawley rats were randomly assigned to three groups: control group,smoking group and smoking cessation group.The rats in control group were placed in a homemade box but free of smoke.The rats in smoking group were exposed to cigarette smoke 1h×2 times per day for 8 weeks.Smoking cessation group: cigarette smoke exposure for 8 weeks was as the same as the smoking group,then without smoke exposure for 2 weeks.All of rats were anesthetized with pentobarbital sodium by intraperitoneal injection,the effect of cigarette smoking on the genioglossus contractile function was analyzed by comparing the Electromyography(EMG)and twitch characters detected by stimulating hypoglossal nerve.The items included electromyography(EMG)amplitude,integrated electromyography(i EMG),Standardized maximum isometric contraction strength(SMIC,maximum isometric contraction strength /Cross-sectional area),Standardized tetanic contraction strength(STC,tetanic contraction strength/Cross-sectional area),fatigue index(FI)of tetanic contraction at the 20 s,40s,80 s and 120 s.The expression of m RNAs and proteins,MHC I,MHCⅡa,MHCⅡx and MHCⅡb,were determine by quantitative real-time RT-PCR and western bloting.Results: 1.Compared with the control group,the EMG amplitude and i EMG in smoking group and smoking cessation group were both lower(P<0.05);Compared with the smoking group,the EMG amplitude and i EMG were higher in the smoking cessation group(P<0.05).2.There were no significant difference in the SMIC and the STC in the three group of rats(P>0.05).3.Compared with the control group,The FI of the smoking group and the smoking cessation group were both lower at each time point(P<0.05);Compared with the smoking group,the FI was higher in the smoking cessation group at each time point(P<0.05).4.HE staining results: HE staining in lung tissue: Normal lung tissue structure in the control group;There were obvious Inflammatory cell infiltration in the lung tissue of the smoking group rats,it was seen that some alveolar wall broke and merged to form a bulla and airway smooth muscle thickened;The lung tissue in the smoking cessation group: pulmonary bulla and thickened airway smooth muscle were still visible,but the lesions slightly reduced compared with the smoking group.HE staining of genioglossus tissue: Normal muscle tissue structure in the control group;Muscle fiber atrophy in the smoking group;Muscle fiber atrophy was still visible in the smoking cessation group,but the degree was reduced compared with the smoking group.5.m RNA expression of MHC isoforms: compared with the control group,the MHC I m RNA expression level in the smoking group was lower(P<0.05),and the smoking cessation group was higher(P<0.05);Compared with the smoking group,the MHC I m RNA expression level of the smoking cessation group was higher(P<0.05);Compared with the control group,the MHCⅡa m RNA expression level of the smoking group was lower(P<0.05),and the smoking cessation group was higher(P<0.05).Compared with the smoking group,the smoking cessation group MHCⅡa m RNA expression level was higher(P<0.05);Compared with the control group,the smoking group MHCⅡx m RNA expression level was higher(P <0.05),and the smoking cessation group was lower(P<0.05);Compared with the smoking group,the MHCⅡx m RNA expression level of the smoking cessation group was lower(P<0.05);Compared with the control group,the MHCⅡb m RNA expression level in the smoking group was higher(P<0.05),and the smoking cessation group was Lower(P<0.05);Compared with the smoking group,the MHCⅡb m RNA expression of the smoking cessation group was lower(P<0.05).6.Protein expression level of myosin heavy chain isoforms: Compared with the control group,the MHC I protein expression were both lower in the smoking group and the smoking cessation group(P <0.05);Compared with smoking group,the MHC I protein expression in smoking cessation group was higher(P<0.05);Compared with the control group,the expression of MHCⅡa protein in the smoking group was lower(P<0.05),and the smoking cessation group was higher(P<0.05);Compared with the smoking group,the expression of MHCⅡa protein in smoking cessation group was higher(P<0.05);Compared with the control group,the expression of MHCⅡx protein in smoking group was higher(P<0.05),and the smoking cessation group was lower(P<0.05);Compared with the smoking group,the expression of MHCⅡx protein in the smoking cessation group was lower(P<0.05);Compared with the control group,the expression of MHCⅡb protein in smoking group was higher(P<0.05),and the smoking cessation group was lower(P<0.05);Compared with the smoking group,the MHCⅡb protein expression in the smoking cessation group was lower(P<0.05).Conclusion: 1.Cigarette smoke exposure for 8 weeks may reduce the fatigue resistance of genioglossus,and which may be partly reversed after smoking cessation for 2 weeks;2.The decrease in fatigue resistance of genioglossus caused by cigarette smoke exposure may associate with the conversion of MHC isoforms to type II,and which may be partly reversed after smoking cessation.