外源性谷氨酰胺合成酶对豚鼠耳蜗电位和超微结构的影响

Effect of Ectogenetic Glutamine Synthetase on Cochlear Potentials and Ultrastructure in Guinea Pig

目的观察外源性谷氨酰胺合成酶对豚鼠耳蜗电位和超微结构的影响。方法健康杂色豚鼠30只,随机分为3组,应用豚鼠全耳蜗灌流技术,分别经耳蜗灌流人工外淋巴液和不同浓度的谷氨酰胺合成酶2小时,记录灌流前和灌流后的耳蜗电位;同时应用透射电镜技术观察灌流前后耳蜗形态学的变化。结果灌流人工外淋巴液后豚鼠耳蜗电位及形态学无改变。灌流0.5U/L谷氨酰胺合成酶后耳蜗微音电位(cochlear microphonics,CM)非线性特点无改变,但其幅度略有下降,听神经复合动作电位(compound action potential,CAP)阈移为5.50±3.33dB;灌流1U/L谷氨酰胺合成酶后CM非线性特点无改变,其幅度下降较灌流0.5U/L谷氨酰胺合成酶时明显,CAP的阈移为10.00±4.17dB,灌流谷氨酰胺合成酶后耳蜗内、外毛细胞的形态和结构未见改变。结论内毛细胞兴奋性神经递质谷氨酸被谷氨酰胺合成酶过量摄取后引起了传入神经功能的改变(CAP阈值升高),证明耳蜗谷氨酸-谷氨酰胺循环中确实有谷氨酰胺合成酶的作用。

Objective To investigate the effect of ectogenetic glutamine synthetase on the cochlear potentials and morphology in guinea pig. Methods 30 healthy guinea pigs were divided into three groups and each consisted of 10 animals. During whole cochlear infusion,the fnnedonal properties of the cochlear were measured by CM and CAP; the morphology of the cochlear was examined by transmission electron microscope. Results After glutamine synthetase perfusion, CM input/output （I/O） function maintained a nonhnear characteristic, but the amplitude of CM declined. The average CAP threshold was elevated 5.50 ± 3.3 dB after 0.5 U/L glutamine synthetase perfusion and increased 10.00± 4.17 dB after 1 U/L glutamine synthetase perfusion. The inner hair cells （IHCs） and outer hair cells （OHCs） appeared normal after glutamine synthetase infusion. Conclusion The glutamine synthetase catalyses the conversions of glutamate to glutamine, which has confirmed the existence of glutamateglutamine cycle in the cochlear.