Gurney A M, Tsien R Y, Lester H A
Proc Natl Acad Sci U S A. 1987 May;84(10):3496-500. doi: 10.1073/pnas.84.10.3496.
Although Ca2+ is a well-established intracellular messenger, there are many questions concerning the kinetics and spatial localization of its effects. Such problems may now be approached with the photosensitive Ca2+ chelator nitr-5. The Ca2+ affinity of this molecule decreases by a factor of 40 after absorption of near-UV light; Ca2+ is liberated with a time constant of approximately equal to 300 microseconds. Nitr-5 or the related compounds nitr-2 and nitr-7, complexed with Ca2+, were introduced into rat sympathetic ganglion cells by dialysis from a patch pipette electrode operating in the whole-cell, voltage-clamp mode. Light flashes released Ca2+ and activated a K+ current. Flash-induced current relaxations followed a simple exponential time course with time constants as brief as 5 ms. Comparison of the kinetics among the chelators, which photolyze at different rates, suggests that release of Ca2+ from nitr-5 is too fast to limit the relaxation. Thus we confirm directly that Ca2+ can modulate membrane properties within a few milliseconds after entering a cell. A preliminary kinetic description of K+ current activation by Ca2+ in rat sympathetic neurons is presented; Ca2+ appears to bind to the channel with a rate constant of at least 2 X 10(7) M-1 X s-1.
尽管钙离子是一种公认的细胞内信使，但关于其作用的动力学和空间定位仍存在许多问题。现在可以用光敏钙离子螯合剂nitr-5来解决这些问题。该分子在吸收近紫外光后，其对钙离子的亲和力降低40倍；钙离子以约300微秒的时间常数被释放出来。将与钙离子结合的nitr-5或相关化合物nitr-2和nitr-7，通过在全细胞电压钳模式下操作的膜片吸管电极进行透析，引入大鼠交感神经节细胞。光脉冲释放钙离子并激活钾离子电流。光脉冲诱导的电流松弛遵循简单的指数时间进程，时间常数短至5毫秒。对以不同速率光解的螯合剂之间的动力学进行比较，表明从nitr-5释放钙离子的速度太快，不会限制松弛。因此，我们直接证实钙离子进入细胞后几毫秒内就能调节膜特性。本文给出了大鼠交感神经元中钙离子激活钾离子电流的初步动力学描述；钙离子似乎以至少2×10⁷ M⁻¹×s⁻¹的速率常数与通道结合。
