Gottlob I, Wündsch L, Tuppy F K
Institute for General and Comparative Physiology, University of Vienna, Austria.
Vision Res. 1988;28(2):203-10. doi: 10.1016/0042-6989(88)90147-2.
Previous studies reported that the ERG b-wave is generated by changes of membrane potential of the Müller Cell, mediated by a proximal and a distal extracellular [K+] increase. From measurements with K+ sensitive electrodes there is some evidence that the proximal K+ source is generated by amacrine cell activity. It has been shown autoradiographically that in the rabbit retina GABA is located within a subgroup of amacrine cells, in interplexiform cells and horizontal cells. The effects of GABA, picrotoxin and bicuculline on the ERG of the isolated superfused retina were investigated. Picrotoxin between 10(-4) and 10(-3) M/l and bicuculline between 10(-5) and 10(-4) M/l enhanced the a- and b-wave amplitudes. The b-wave peaked at a later time and decayed at a slower rate than did the control ERG. In higher concentrations than 10(-5) M/l GABA had the opposite effect. In experiments with isolation of the PIII by means of 10(-2) M/l Aspartate or lowering of temperature to 22 degrees C, no effect of GABA on PIII could be shown. The present investigation supports participation of GABAergic cells in b-wave generation. As an underlying mechanism a proximal K+ source is assumed, which is modified by amacrine cell activity.
先前的研究报道，视网膜电图b波是由米勒细胞的膜电位变化产生的，由细胞外近端和远端[K+]升高介导。通过钾离子敏感电极测量发现，有证据表明近端钾离子来源是由无长突细胞活动产生的。放射自显影显示，在兔视网膜中，γ-氨基丁酸（GABA）存在于无长突细胞亚群、网间细胞和水平细胞中。研究了GABA、印防己毒素和荷包牡丹碱对离体灌注视网膜电图的影响。10^(-4)至10^(-3)M/L的印防己毒素和10^(-5)至10^(-4)M/L的荷包牡丹碱可增强a波和b波振幅。与对照视网膜电图相比，b波峰值出现时间更晚，衰减速度更慢。浓度高于10^(-5)M/L时，GABA则产生相反的效果。在使用10^(-2)M/L天冬氨酸分离PIII或将温度降至22℃的实验中，未显示GABA对PIII有影响。本研究支持了GABA能细胞参与b波产生。作为一种潜在机制，假定存在一个近端钾离子来源，其会被无长突细胞活动所改变。
