Highly Selective Rapid Calcium Chelators

BAPTA and BAPTA-Na₄ are highly selective chelators for Ca²⁺ over Mg²⁺.^1,2) BAPTA and BAPTA-Na₄ are EGTA derivatives whose carbon chains between oxygen and nitrogen atoms are replaced with benzene rings. Their selectivity for Ca²⁺ is higher than EGTA’s and the binding does not depend on pH. Their chelation reactions are more rapid than that of EGTA, thus, it has been reported that the distances between Ca²⁺ channels and Ca²⁺ sensors in neurons can be evaluated by analyzing the transmitter release inhibition by different chelators.³⁾ While both BAPTA and BAPTA-Na₄ are membrane-impermeable, BAPTA-AM, a BAPTA ester, is membrane-permeable and can chelate with Ca²⁺ in cells after the hydrolysis by intracellular esterases.⁴⁾ In this way, BAPTA, BAPTA-Na₄ and BAPTA-AM are valuable tools to study the role of calcium in cell signaling.