Activation of a potassium current by rapid photochemically generated step increases of intracellular calcium in rat sympathetic neurons.

Publisher Website
Google Scholar
Abstract
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 .apprxeq. 300 .mu.s. 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 .times. 107 M-1 .cntdot. s-1.