Kinetic Properties of DM-Nitrophen Binding to Calcium and Magnesium

• Published in: Biophysical journal Vol. 88; no. 6; pp. 4421 - 4433
• Main Authors: Faas, Guido C., Karacs, Kinga, Vergara, Julio L., Mody, Istvan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2005; Biophysical Society
• Subjects: Acetates - metabolism; Biochemistry; Biophysical Phenomena; Biophysics; Calcium; Calcium - metabolism; Calcium Signaling; Cellular biology; Egtazic Acid - analogs & derivatives; Egtazic Acid - metabolism; Electrophysiology; Ethylenediamines - metabolism; In Vitro Techniques; Kinetics; Magnesium; Magnesium - metabolism; Models, Biological; Photolysis; Physical properties
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.104.057745

Caged-Ca 2+ compounds such as nitrophenyl-EGTA (NP-EGTA) and DM-nitrophen (DMn) are extremely useful in biological research, but their use in live cells is hampered by cytoplasmic [Mg 2+]. We determined the properties of Ca 2+ release from NP-EGTA and DMn by using Oregon green BAPTA-5N to measure changes in [Ca 2+] after ultraviolet flash photolysis in vitro, with or without Mg 2+ present. A large fraction (65%) of NP-EGTA, which has a negligible Mg 2+ affinity, uncages with a time constant of 10.3 ms, resulting in relatively slow increases in [Ca 2+]. Uncaging of DMn is considerably faster, but DMn has a significant affinity for Mg 2+ to complicate the uncaging process. With experimentally determined values for the Ca 2+ and Mg 2+ binding/unbinding rates of DMn and NP-EGTA, we built a mathematical model to assess the utility of NP-EGTA and DMn in rapid Ca 2+-uncaging experiments in the presence of Mg 2+. We discuss the advantages and disadvantages of using each compound under different conditions. To determine the kinetics of Ca 2+ binding to biologically relevant Ca 2+ buffers, such as Ca 2+-binding proteins, the use of DMn is preferable even in the presence of Mg 2+.