title: Laser photolysis of caged calcium: rates of calcium release by nitrophenyl-EGTA and DM-nitrophen.
abstract: Nitrophenyl-EGTA and DM-nitrophen are Ca2+ cages that release Ca2+ when cleaved upon illumination with near-ultraviolet light. Laser photolysis of nitrophenyl-EGTA produced transient intermediates that decayed biexponentially with rates of 500,000 s-1 and 100,000 s-1 in the presence of saturating Ca2+ and 290,000 s-1 and 68,000 s-1 in the absence of Ca2+ at pH 7.2 and 25 degrees C. Laser photolysis of nitrophenyl-EGTA in the presence of Ca2+ and the Ca2+ indicator Ca-orange-5N produced a monotonic increase in the indicator fluorescence, which had a rate of 68,000 s-1 at pH 7.2 and 25 degrees C. Irradiation of DM-nitrophen produced similar results with somewhat slower kinetics. The transient intermediates decayed with rates of 80,000 s-1 and 11,000 s-1 in the presence of Ca2+ and 59,000 s-1 and 3,600 s-1 in the absence of Ca2+ at pH 7.2 and 25 degrees C. The rate of increase in Ca(2+)-indicator fluorescence produced upon photolysis of the DM-nitrophen: Ca2+ complex was 38,000 s-1 at pH 7.2 and 25 degrees C. In contrast, pulses in Ca2+ concentration were generated when the chelator concentrations were more than the total Ca2+ concentration. Photoreleased Ca2+ concentration stabilized under these circumstances to a steady state within 1-2 ms.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201, USA.
authors.forename: G C
authors.initials: GC
authors.lastname: Ellis-Davies
authors.forename: J H
authors.initials: JH
authors.lastname: Kaplan
authors.forename: R J
authors.initials: RJ
authors.lastname: Barsotti
mesh_terms: D000085:Acetates / Q000737:chemistry / Q000528:radiation effects*; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000008:administration & dosage*; D002614:Chelating Agents / Q000737:chemistry / Q000528:radiation effects*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D005029:Ethylenediamines / Q000737:chemistry / Q000528:radiation effects*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007700:Kinetics; D007834:Lasers; D008956:Models, Chemical; D009930:Organic Chemicals; D010782:Photolysis; D013696:Temperature
chemical_list: D000085:Acetates; D002614:Chelating Agents; D005029:Ethylenediamines; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D009930:Organic Chemicals; C071335:calcium orange; C057014:DM-nitrophen; C085112:2-nitrophenyl-EGTA; D004533:Egtazic Acid; D002118:Calcium