BAPTA is a calcium-selective chelator developed by Dr. Tsien. It has logKCa=6.97 and logKMg=1.77. The basic chelating unit resembles that of EGTA, but the two aliphatic nitrogen atoms are replaced by aromatic nitrogen. Thus, BAPTA is not protonated at physiological pH. BAPTA possesses pKa3=5.47 and pKa4=6.36. This property indicates that the deprotonation step is not included in its calcium complexation step, and it has a higher complexation rate than EGTA because it is not affected by proton interference. BAPTA-AM is an acetoxymethyl ester derivative of BAPTA that can be easily loaded into cells using the AM method. BAPTA-AM is useful for controlling the intracellular calcium concentration.
Hydrolysis of AM ester
1) R. Y. Tsien, New Calcium Indicators and Buffers with High Selectivity against Magnesium and Protons: Design, Synthesis, and Properties of Prototype Structures. Biochemistry. 1980;19:2396-2404.
2) R. Y. Tsien, A Non-disruptive Technique for Loading Calcium Buffers and Indicators into Cells. Nature. 1981;290:527-528.
3) J. I. Korenbrot, et al., The Use of Tetracarboxylate Fluorescent Indicators in the Measurement and Control of Intracellular Free Calcium Ions. Soc Gen Physiol Ser. 1986;40:347-363.
4) S. M. Harrison, et al., The Effect of Temperature and Ionic Strength on the Apparent Ca-affinity of EGTA and the Analogous Ca-chelators BAPTA and Dibromo-BAPTA. Biochim Biophys Acta. 1987;925:133-143.
5) E. W. Gelfand, et al., Dissociation of Unidirectional Influx of External Ca2+ and Release from Internal Stores in Activated Human T Lymphocytes. Eur J Immunol. 1990;20:1237-1241.
6) J. P. Kao, et al., Active Involvement of Ca2+ in Mitotic Progression of Swiss 3T3 Fibroblasts. J Cell Biol. 1990;111:183-196.
7) M. L. Schubert, et al., Functionally Distinct Muscarinic Receptors on Gastric Somatostatin Cells. Am J Physiol. 1990;258:G982-G987.
8) Y. Tojyo, et al., Inhibitory Effects of Loading with the Calcium-chelator 1, 2-Bis(o-aminophenoxy)ethane-N, N, N E N Etetraacetic acid (BAPTA) on Amylase Release and Cellular ATP Level in Rat Parotid Cells. Biochem Pharmacol. 1990;39:1775-1779.