Rate of Release of Ca2+following Laser Photolysis of the DM-nitrophen-Ca2+Complex

Abstract

The determination of the rate of release of Ca2+by pulsed photolysis of the photolabile chelator DM-nitrophen is important for its use in time-resolved physiological studies: the rate of substrate or effector release should be faster than the processes they initiate. Flash photolysis of DM-nitrophen using a 50-ns pulse from a frequency-doubled ruby laser (with emission at 347 nm having energy of ca. 10-20 mJ) yields short-lived photo-chromic or aci-nitro intermediates. At pH 6.9, double-exponential decay of a photo-chromic intermediate was observed for DM-nitrophen itself and its Ca2+complex (7-1/2 values of 24 and 570 µs, and 32 and 220 µs respectively), while only monoexponential decay of the DM-nitrophen-Mg2+complex was detected (T½ = 31 µs). Only the photochemistry of DM-nitrophen-Ca2+was found to be pH sensitive (monoexponential decay, T½~ 115 µfis at pH 7.9 and 8.9). Use of the Ca2+-sensitive metallochromic dye antipyrylazo III in conjunction with pulsed photolysis of DM-nitrophen-Ca2+enabled an upper limit of the half-time of release of Ca2+to be established of ca. 180 /xs (the rate of association of Ca2+with the dye was probably rate determining). The rate of Ca2+photorelease may, however, be faster than this. Thus, the DM-nitrophen-Ca2+complex releases Ca2+on photolysis sufficiently rapidly for the study of many Ca2+-dependent physiological processes with improved kinetic resolution over conventional mixing methods. © 1992, American Chemical Society. All rights reserved.