Photophysical study of the Ca2+ indicator Fura-2 and the K+ indicator PBFI

摘要

The fluorescent indicators Fura-2 and PBFI are widely used for the determination of intracellular concentrations of Ca$+2$PLU$/ and K$+$PLU$/, respectively. To investigate the complex forming reaction between Fura-2 and Ca$+2$PLU$/, and between PBFI and K$+$PLU$/ in the ground and excited states, steady-state and time-resolved measurements were performed. The fluorescence decay surfaces were analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution: (1) for Fura-2: k$-01$/ $EQ 1.2 $MUL 10$+9$/ s$+$MIN@1$/, k$-21$/ $EQ 1.0 $MUL 10$+11$/ M$+$MIN@1$/x$+$MIN@1$/, k$-02$/ $EQ 5.5 $MUL 10$+8$/s$+$MIN@1$/, k$-12$/ $EQ 2.2 $MUL 10$+7$/s$+$MIN@1$/ (2) for PBFI: k$-01$/ $EQ 1.1 $MUL 10$+9$/s$+$MIN@1$/, k$-21$/ $EQ 2.7 $MUL 10$+8$/M$+$MIN@1$/s$+$MIN@1$/, k$-02$/ $EQ 1.8 $MUL 10$+9$/s$+$MIN@1$/, k$-12$/ $EQ 1.4 $MUL 10$+9$/s$+$MIN@1$/ k$- 01$/ and k$-02$/ denote the deactivation rate constants of the free and bound forms of the indicator, respectively k$-21$/ represents the bimolecular rate constant of binding of the cation by the indicator whereas k$-12$/ is the rate constant of dissociation of the cation:indicator complex. For both probes the effect of the excited-state reaction can be neglected in the determination of K$-d$/ and/or the ion concentration.