Tuning caged calcium: photolabile analogues of EGTA with improved optical and chelation properties.
The physico-chemical properties of several Ca(2+)-selective, photolabile chelators are described. These molecules have been developed as part of an effort to produce a caged Ca(2+) that improved upon the Ca(2+) chelation properties and light absorption capability of nitrophenyl-EGTA (NP-EGTA). Four dimethoxy-ortho-nitrophenyl derivatives of EGTA (called DMNPE-1 through -4), and one analogue of EGTA (DMNPE-5) have been characterized, each of which is bisected upon irradiation. One of these cages has a higher affinity than NP-EGTA: DMNPE-4 has a K(d) for Ca(2+) of 48 nm at pH 7.2 (19 nM at pH 7.4). Furthermore, this cage has a large extinction coefficient of 5120 M(-1)cm(-1) at 350 nm (cf. 975 M(-1)cm(-1) for NP-EGTA). The other physico-chemical properties of DMNPE-4 are: quantum yield of photolysis of 0.09; bipasic Ca(2+) release kinetics (70% released with a rate of about 48,000 s(-1) and 30% at 1.5s(-1)) and photoproducts that bind Ca(2+) with very low affinity (K(d) in the range of 2mM, pH 7.2), hence most of the bound Ca(2+) is released rapidly and efficiently upon photolysis. Thus, DMNPE-4 has a unique combination of properties that make it an extremely effective Ca(2+) cage.
Ellis-Davies
Graham C R
GC
Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA. ged@drexel.edu
Barsotti
Robert J
RJ
D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000378:metabolism; D002614:Chelating Agents / Q000032:analysis / Q000737:chemistry*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D005456:Fluorescent Dyes / Q000032:analysis / Q000737:chemistry; D006801:Humans; D050417:Insulin-Secreting Cells / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D008027:Light; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D010777:Photochemistry; D010782:Photolysis; D013997:Time Factors
D002614:Chelating Agents; D005456:Fluorescent Dyes; C117677:dimethoxynitrophenyl-EGTA-4; C085112:2-nitrophenyl-EGTA; D004533:Egtazic Acid; D002118:Calcium