NEW FLUORESCENT CALCIUM INDICATORS DESIGNED FOR CYTOSOLIC RETENTION OR MEASURING CALCIUM NEAR MEMBRANES

A new family of fluorescent calcium indicators has been developed base d on a new analog of BAPTA called FF6. This new BAPTA analog serves as a versatile synthetic intermediate for developing Ca2+ indicators tar geted to specific intracellular environments. Two of these new Ca2+ in dicators, fura-PE3 and fura-FFP18, are described in this report. Fura- PE3 is a zwitterionic indicator that resists the rapid leakage and com partmentalization seen with fura-2 and other polycarboxylate calcium i ndicators. In contrast to results obtained with fura-2, cells loaded w ith PE3 remain brightly loaded and responsive to changes in concentrat ion of cytosolic free calcium for hours. Fura-FFP18 is an amphipathic indicator that to binds to liposomes and to cell membranes. Studies to be detailed later indicate that FFP18 functions as a near-membrane Ca 2+ indicator and that calcium levels near the plasma membrane rise fas ter and higher than in the cytosol.