EXTRACELLULAR PH IN THE ISOLATED RETINA OF THE TOAD IN DARKNESS AND DURING ILLUMINATION
EXTRACELLULAR PH IN THE ISOLATED RETINA OF THE TOAD IN DARKNESS AND DURING ILLUMINATION
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DOI：
10.1113/jphysiol.1989.sp017876
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发表时间：
1989-12-01
影响因子：
5.5
通讯作者：
WEN, R
中科院分区：
文献类型：
--
作者：
OAKLEY, B;WEN, R
1.用H(+)选择性微电极测定了中华大蟾蜍视网膜组织的胞外pH(Pho)。在用缓冲能力较低的磷酸盐缓冲液(pH 7.8)灌流时，视网膜内的pho为7.0-7.2，整个视网膜远端存在一个pho梯度，并进入浴液中。2.视网膜的酸度似乎部分是由于糖酵解和ATP水解的联合反应，因为缺氧显著增加了pho梯度，而无葡萄糖的丙酮酸溶液或毛花蛇舌草素灌流降低了这一梯度。3.维持光照可引起近端视网膜的酸化和远端视网膜的碱化。阻断向二级神经元(1.0 mM-天冬氨酸)的突触传递减少了酸化，但对碱化几乎没有影响，这与碱化来自受体，而酸化来自受体后的观点是一致的。4.视网膜神经元通过Na(+)-H+交换产生大量的酸，这是因为Na(+)-H+交换阻滞剂2 mM-阿米洛利在黑暗中引起持续的碱化，减少了光诱发的PHO变化，而氯离子-HCO3-交换阻滞剂1.0 mM‐4‐acetamido‐4‘‐isothiocyanatostilbene‐2.2’‐disulphonic酸(SITS)产生的碱性作用要小得多。5.切换到缓冲容量是磷酸盐缓冲溶液的75倍的碳酸氢盐缓冲溶液会导致视网膜pho变得不那么酸性，并显著降低光诱发的pho变化的幅度。6.在碳酸氢盐缓冲溶液中加入2.0 mM-乙酰唑胺，增加了pho梯度和光诱导的pho变化。这些数据与碳酸氢酶的观点是一致的，碳酸氢酶集中在Müler(神经胶质)细胞中，在水平细胞中程度较小，增加了碳酸氢盐缓冲系统的有效性。7.从碳酸氢盐缓冲溶液切换到磷酸盐缓冲溶液会减弱视网膜电波的b波，这很可能是通过酸化磷酸盐来实现的。总体而言，我们的结果强调了碳酸氢盐缓冲系统在光和暗条件下可变酸度挤出期间缓冲磷酸盐的重要性。
1. Extracellular pH (pHo) was measured in the isolated retina preparation of the toad, Bufo marinus, using H(+)‐selective microelectrodes. During superfusion with phosphate‐buffered solution (pH 7.8), which had a low buffering capacity, pHo in the inner retina was 7.0‐7.2 and there was a pHo gradient throughout the distal retina and into the bathing solution. 2. The retinal acidity appears to be due in part to the combined reactions of glycolysis and ATP hydrolysis, since anoxia greatly increased the pHo gradient, while superfusion with either glucose‐free pyruvate solution or strophanthidin decreased this gradient. 3. Maintained illumination evoked both an acidification in the proximal retina and an alkalinization in the distal retina. Blocking synaptic transmission to second‐order neurones (1.0 mM‐aspartate) decreased the acidification but had little effect on the alkalinization, consistent with the notion that the alkalinization is of receptoral origin, while the acidification is of post‐receptoral origin. 4. Retinal neurones extrude a significant amount of acid via Na(+)‐H+ exchange, since 2.0 mM‐amiloride, a blocker of Na(+)‐H+ exchange, caused a sustained alkalinization in darkness and decreased the light‐evoked changes in pHo, while 1.0 mM‐4‐acetamido‐4'‐isothiocyanatostilbene‐2.2'‐disulphonic acid (SITS), a blocker of Cl(‐)‐HCO3‐ exchange, produced a much smaller alkalinization. 5. Switching to a bicarbonate‐buffered solution having a 75 times greater buffering capacity than the phosphate‐buffered solution caused retinal pHo to become less acidic and significantly decreased the amplitude of the light‐evoked pHo changes. 6. Addition of 2.0 mM‐acetazolamide, a carbonic anhydrase inhibitor, to the bicarbonate‐buffered solution increased both the pHo gradient and the light‐evoked changes in pHo. These data are consistent with the idea that carbonic anhydrase, which is concentrated in Müller (glial) cells and to a lesser extent in horizontal cells, increases the effectiveness of the bicarbonate buffer system. 7. Switching from bicarbonate‐buffered to phosphate‐buffered solutions attenuated the b‐wave of the electroretinogram, most likely by acidifying pHo. Overall, our results emphasize the importance of the bicarbonate buffer system in buffering pHo during periods of variable acid extrusion in light and in darkness.