Effects Of Mild Hypothermia Combination With Dexmedetomidine On Myocardium Monophasic Action Potential And The Expression Of Connexin43

Objective:To exploring the effects of mild hypothermia combined with dexmedetomidine on myocardium monophasic action potential and the expression of Cx43,To discussing its possible mechanism.Methods: 18 adult New Zealand rabbits,2.0~2.5kg,were randomly divided into three groups(n=6).When a rabbit was successfully anesthetized,its chest cavity was opened and the heart was carefully excised.The isolated heart was placed on a Langerdorff perfusion system.After the 15 min balanced perfusion,the control group(group C)underwent continuous perfusion with K-H solution(37?)for 60 min.The hypothermia group(group H)underwent continuous perfusion with K-H solution(32?)for 60 min,and the hypothermia plus dexmedetomidine group(group HD)underwent continuous perfusion with K-H solution(32?)and dexmedetomidine 25 ?g/L for 60 min.Recording the heart rate(HR)and the three layer myocardium monophasic action potential(MAP)of heart after balanced perfusion 15 min(T0)and continued perfusion 15,30,60 min(T1-3).Calculating the monophasic action potential amplitude(MAPA),the maximal velocity of depolarization(Vmax),the duration of repolarization at 50% and 90%(MAPD50,MAPD90)and transmural disperse of repolarization(TDR).Following perfusion,sections of the left anterior ventricular wall were taken,Western blot and immunohistochemistry staining performed to detect the protein expression of Cx43.Results:1.The comparison of HR: Group H and Group HD showed slower HR at T1-3 than T0(P<0.05),The comparisons between Group H and Group HD showed no statistically significant difference(P>0.05).2.The comparison of MAPs:(1)The comparison of MAPD50:At T1-3,Group H and Group HD showed longer MAPD50 than Group C in three layers of myocardium(P < 0.05),but the comparisons between Group H and Group HD showed no statistically significant difference(P>0.05).(2)The comparison of MAPD90: At T1-3,Group H and Group HD showed longer MAPD90 than Group C in three layers of myocardium(P < 0.05),but the comparison between Group H and Group HD showed no statistically significant difference(P>0.05).(3)The comparisons of TDR:At T1-3,Group H and Group HD showed increased TDR than Group C(P < 0.05),but comparisons between Group H and Group HD showed no statistically significant difference(P > 0.05).(4)The comparison of MAPA:There were no statistically differences in MAPA among groups(P>0.05).(5)The comparison of Vmax:There were no statistically differences in Vmax among groups(P > 0.05).3.The result of Cx43:(1)The results of Western blot:The Cx43 protein expression was markedly decreased in Group H and Group HD(P < 0.05).The comparisons between Group H and Group HD were no statistically significant difference(P>0.05).(2)The results of immunohistochemistry:group C,the positive expression uniform distributed in the cardiac muscle tissue and express a lot;group H,there are a less and anomaly positive expression of Cx43 in the cardiac muscle tissue;group HD,there are few and confusedly positive expression of Cx43 in the cardiac muscle tissue.Conclusion:The decreased expression and abnormal distribution of Cx43 may be the reason influence the cardiac electrophysiology caused by mild hypothermia.However,dexmedetomidine 25 ?g/L will not influence the changes caused by hypothermia.