摘要
Objective To investigate the effect of D-AP5 (D-2-amino-5-phosphonopentanoate, a specific NMDA-antagonist) on the increase of intracellular free Ca 2+ concentration ([Ca 2+ ] i) induced by glutamate in isolated cochlear inner hair cells (IHCs), and to detect the autoreceptors of the IHC membrane. Methods When a laser scanning confocal microscope (LSCM) was used, the exogenous glutamate (Glu)-induced changes in [Ca 2+ ] i of isolated IHCs and OHCs of guinea pig cochlea were observed with fluo-3, a fluorescent probe for [Ca 2+ ] i. After D-AP5 or CNQX (6--cyano--7--nitroguinoxaline--2, 3--dione, a specific AMPA- antagonist) was administrated, the exogenous glutamate (Glu)-induced changes in [Ca 2+ ] i of isolated IHCs were recorded. Results In the presence of a low concentration Glu (3.85?μmol/L), there was an increase of [Ca 2+ ] i in IHCs, whereas there was no change in OHCs. When 50?μmol/L of D-AP5 was administrated in advance, Glu did not induce a corresponding increase in [Ca 2+ ] i in IHCs, and 50?μmol/L of CNQX did not completely block the increase of [Ca 2+ ] i in IHCs. Conclusions These results suggest that the autoreceptors existing in the IHC membrane are mainly of NMDA type, while there are relatively few AMPA receptors. Exogenous Glu is capable of increasing [Ca 2+ ] i in IHCs by acting on the NMDA autoreceptor of IHCs in a positive feedback manner.
目的 探讨谷氨酸 (glutamate ,Glu)受体拮抗剂D AP5 (D 2 amino 5 phosphonopentanoate)和CNQX (6 cyano 7 nitroguinoxaline 2 ,3 dione)对Glu调节耳蜗内毛细胞 (innerhailcells ,IHC)游离钙 ([Ca2 + ]i)浓度的影响。方法 在激光共聚焦显微镜下用荧光染料Fluo 3作为指示剂 ,先观察外源性Glu对离体耳蜗IHC胞内 [Ca2 + ]i 浓度的调节作用 ,然后观察D AP5和CNQX对这种调节作用的影响。结果 Glu可增高离体耳蜗IHC内 [Ca2 + ]i 浓度。然而 ,当预先加入 5 0 μmol/L的D AP5时 ,离体耳蜗IHC胞内[Ca2 + ]i 不再增高 ;而预先加入 5 0 μmol/L的CNQX时 ,离体耳蜗IHC胞内 [Ca2 + ]i 仍增高。结论 耳蜗IHC上存在Glu自身受体 ,可能主要为NMDA型 ,AMPA型较少。外源性谷氨酸可以通过耳蜗内毛细胞NMDA自身受体以正反馈方式引起游离钙的增加。
