Investigation on the transmitter substance released from vertebrate photoreceptors.

虽然脊椎动物光感受器的递质还不清楚，但间接证据表明天冬氨酸或谷氨酸可能是递质。本研究采用机械分离法分离鲤鱼视网膜视杆细胞，以鉴定视杆细胞释放的递质物质。20%至80%的分离杆保留其轴突，并且25%至50%的分离杆具有轴突终末。用已知化学和离子组成的溶液灌注这些细胞。用高效液相色谱法分析从杆释放到灌注溶液中的氨基酸。虽然我们预期在黑暗中释放天冬氨酸或谷氨酸，但我们观察到几乎所有氨基酸的释放。此外，这些氨基酸的释放不受光刺激的影响。另一方面，当用高K ^+溶液或低Ca^<2+>溶液处理细胞使其去极化时，则促进了释放。再说一次，这是不具体的。这种“去极化诱导的释放”不需要Ca^<2+>的存在，因为在Co^<2+>存在和Ca^<2+>不存在的情况下，我们仍然观察到氨基酸释放的增加。虽然分离的视杆保留轴突或轴突末端，但我们不确定这些细胞是否从位点释放这些氨基酸，而这些氨基酸实际上参与了完整细胞中递质的释放。在我们的制备中，能够以光依赖性方式释放递质的完整细胞的数量可能太少了。然而，目前的工作确实表明，常规标准-去极化时物质的释放-不足以确定发射器，需要进行仔细研究以解决这一问题。

Though the transmitter of a vertebrate photoreceptor has not been known yet, circumstantial evidence suggests that aspartate or glutanate could be the transmitter. The purpose of this study is to identify the transmitter substance released from rod photoreceptors.Rod photoreceptors were isolated with mechanical dissociation of carp retinas. Twenty to eighty percent of the isolated rods retained their axons and 25 - 50 % of then had axon terminals. These cells were perfused with solutions of known chemical and ionic composition. Amino acids which were released from the rods into the perfusion solution were analyzed with high performance liquid chromatography. Though we expected the release of aspartate or glutagate in the dark, we observed the release of almost all of the amino acids. Moreover, the release of these amino acids was not affected by a light stimulation. On the other hand, when the cells were depolarized with a treatment of a high-K^+ solution or a low Ca^<2+>-solution, the release was facilitated. Again, it was none-specific. This "depolarization-induced release" did not require the presence of Ca^<2+> since in the presence of Co^<2+> and in the absence of Ca^<2+>, we still observed the increase in the amino acid release. Though the isolated rod retained axon or axon terminal, we were not sure whether these cells released these amino acids from the cite which is actually involved in the transmitter release in intact cells. It may be true that the population of the intact cells which could release the transmitter in a light-dependent manner was too low in our preparation. However, the present work did indicate that the conventional criteria --release of the substance upon depolarization-- is not sufficient to identify the transmitter and that careful study is needed to solve this issue.