在不均匀夸张的大鼠隔肌标本上串终板电位初始段衰减的突触前性质(英文)

Presynaptic nature of the initial rundown of tetanic trainof endplate potentials in isolated nonuniform stretched muscle preparation of rats

在大白鼠离体不均匀牵张膈肌标本(INSMP)上可选择接近神经肌接头正常生理状态的终板,同时记录同一终板的小终板电位(MEPP),终板电位(EPP)和微电泳外源性乙酰胆碱(ACh)产生的乙酰胆碱电位(AChP);以AChP为直接的突触后膜兴奋性大小指标,以量子释放参数:量子含量(M)及二项统计参数为突触前递质释放量大小的指标,研究了串终板电位初始段衰减现象的性质.发现在2,10,50和100 Hz间接刺激下,INSMP上串EPPs都发生初始衰减现象;刺激频率增高,衰减更为明显.50 Hz时,在第1,3,5,7,11,25,50,75和100个EPP后20 ms的AChP幅度与EPP之前的AChP幅度无明显差别.100 Hz时,在产生第25,50,75和100个EPP后10 ms的AChP与EPP之前的AChP幅度也无明显差别.直接证明了在产生串EPPs衰减时无突触后膜兴奋性的改变.刺激频率增高,第1个EPP的量子含量(M_1)无变化,EPPs平台期的量子含量(M_x)减小,即刻可释放的量子贮存(n)无变化,平均量子释放机率(P)减少.表明串EPPs初始段的衰减是正常神经肌接头传递的一种自身调节,它完全由突触前量子释放减少引起的,其大小与刺激频率有关.突触前ACh受体可能参与了这种自身调节.

MEPPs,EPPs and AChP were simultaneously recorded from the same endplate in the isolated nonuniform stretched rat hemidiaphragms.By taking AChP as an indicator of postsynaptic sensitivity to ACh and quantal content estimated using direct method and binomial parameters as the indicators of presynaptic quantal release,the nature of initial rundown of train EPPs evoked at 2,10,50 and 100 Hz was investigated.There was initial rundown of short train of EPPs at the frequencies tested.The higher the stimulation frequency,the more significant the initial rundown.The amplitudes of AChPs after the 1st,3rd,5th,7th,11th,25th,50th,75th and 100th EPPs of a train at 50 Hz were almost the same as those before the train.The amplitudes of AChPs after the 25th,50th,75th and 100th EPPs of a train at 100 Hz were also almost the same as those before the train.The mean quantal content of the maintained EPPs(Mx)and the probability of quantal release(P)were decreased as the stimulation frequency was increased.The quantal content of the first EPP(M1)and the immediate available store(n)were not changed with the frequency.In each train of EPPs,Mxwas smaller than M1 The results indicate that there are no changes in postsynaptic sensitivity when the initial rundown occurs.The nature of initial rundown is the result of progressive decline in presynaptic quantal release.