A new method of determining intracellular free Ca2+ concentration using Quin2-fluorescence

Abstract

We determined intracellular free Ca2+ concentration by fluorescence spectroscopy and the time-resolved measurements of 2-[(2-amino-5-methylphenoxy) methyl]-6-methoxy-8-aminoquinoline-N,N,N',N'-tetraacetic acid, tetrapotassium salt (Quin2) incorporated in suspended mouse leukemia L1210 cells. The paper reports the following two points. (1) Various fluorescence spectrum patterns in cell suspensions dissolved with Quin2 acetoxy methylester were compared with those of the complex in buffer solution containing esterase. (2) The fluorescence lifetime of Quin2 bound to Ca2+ was approx. 4.5-11 times longer (10 +/- 1 ns) than that (1.5 +/- 0.5 ns) of Quin2. The fraction of the long lifetime component was plotted against the concentration of CaCl2 in buffer solution. From the results obtained, it was found that approx. 35 nM Ca2+ was contained in each L1210 cell.