Nature. 1986;322(6076):261-3. doi: 10.1038/322261a0.
Measurement of the free calcium concentration within a photo-receptor outer segment has been considered an important aim since the proposal by Hagins and Yoshikami that the primary event in phototransduction is a release of Ca (2+) inside the cell. More recent evidence has cast doubt on the calcium hypothesis, and the observations of Yau and Nakatani and Matthews et al. suggest that the internal Ca (2+) concentration ([Ca (2+)]i), may decrease after a flash of light. In the present study we have measured [Ca (2+)]i directly by using a new method for incorporating the Ca-sensitive photoprotein aequorin into an isolated rod. We report that the light response is accompanied by a decrease in [Ca (2+)]i, caused by the closure of light-sensitive channels which are the main route for Ca (2+) entry into the outer segment. Of the Ca (2+) entering through light-sensitive channels, about 95% is sequestered by a rapid and reversible buffering mechanism. Calcium is removed from the cell by an electrogenic pump in which 3 Na (+) ions are exchanged for each Ca (2+); the pump is highly active and the free Ca (2+) in the cell declines with a time constant of ~0.5 s after a flash of light.
自从 Hagins 和 Yoshikami 提出光感受器外段内游离钙浓度的测量是光传导的首要事件以来，人们一直认为这是一个重要的目标。最近的证据对钙假说提出了质疑，Yau 和 Nakatani 以及 Matthews 等人的观察结果表明，光闪后细胞内的钙离子浓度 ([Ca(2+)]i) 可能会降低。在本研究中，我们使用一种将钙敏感的发光蛋白水母发光蛋白掺入分离的杆状细胞的新方法直接测量了 [Ca(2+)]i。我们报告说，光反应伴随着 [Ca(2+)]i 的降低，这是由光敏感通道的关闭引起的，光敏感通道是 Ca(2+) 进入外段的主要途径。通过光敏感通道进入的 Ca(2+) 中，约 95% 被快速可逆的缓冲机制隔离。钙通过一种电致泵从细胞中排出，其中每 3 个 Na(+) 离子交换 1 个 Ca(2+)；泵的活性很高，光闪后细胞内游离钙的衰减时间常数约为 0.5 秒。
