TEFLabs’ non-fluorescent calcium indicators are BAPTA and its bromine and fluorine derivatives. BAPTA [1,2,-bis(o-aminophenoxy)ethane-N,N,-N’,N’, tetra-acetic acid] forms the basis of all the fluorescent calcium ion indicators. It was derived from EGTA [ethylene glycol bis(β-aminoethyl ether) N,N,N’,N’ tetra-acetic acid] to create a selectivity of 105 for Ca2+ over Mg2+.
BAPTA (X=Y=H) itself is now used essentially for buffering calcium, but the lower affinity fluoro derivatives – difluoro (X=F, Y=H) and tetrafluoro11 (BAPTA FF, X=Y=F), have been a good source for studying high concentration of calcium using F NMR. 5,5’-DimethylBAPTA or “MAPTA” (X=CH3, Y=H) is the highest affinity BAPTA of all. DibromoBAPTA (X=Br, Y=H) has an intermediate affinity and has been used extensively to study calcium mobilization, spatial buffering, and calcium shuttling in many cells. All the BAPTA derivatives are available as potassium salts or free acids and as acetoxymethyl esters. The properties are shown in Table 5.3.
Kd (nM), no Mg+ : 160
solubility: DMSo (AM form), H2O (salt form)
Table 5.3 Non-Fluorescent Calcium Indicators
FIG. 5.5 Bapta and versions structure