Investigation on the transmitter substance released from vertebrate photoreceptors.

虽然脊椎动物的光感受器的传递器还不为人所知，但间接证据表明，天冬氨酸或谷氨酸可能是传递器。本研究的目的是鉴定杆状光感受器释放的递质。用机械解离法分离鱼视网膜的杆状光感受器。20% - 80%的分离的杆状细胞保留了轴突，25% - 50%的杆状细胞有轴突终末。这些细胞被灌注了已知化学和离子组成的溶液。用高效液相色谱法分析从棒中释放到灌注液中的氨基酸。虽然我们期望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+>-溶液处理细胞去极化时，促进了释放。同样，它也没有特异性。这种“去极化诱导释放”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。虽然分离的杆状细胞保留了轴突或轴突末端，但我们不确定这些细胞是否释放了这些氨基酸，而这些氨基酸实际上参与了完整细胞的递质释放。在我们的制备中，能够以依赖光的方式释放发射器的完整细胞的数量可能太少。然而，目前的工作确实表明，传统的标准——在去极化时释放物质——不足以识别发射器，需要仔细研究来解决这个问题。

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.