The Use: of Fura- for Estimating Fluxes

-The compound fura(Grynkiewicz et al., J. Biol. Chem. 260, 344&3450, 1985) is generally known as an indicator dye for measuring the concentration of free calcium ([Ca”]) inside living cells. It should be appreciated, however, that this is not what it actually is. More accurately, it is a divalent metal ion chelator which changes its fluorescence properties upon complexation. Thus, [Ca ‘1 has to be inferred indirectly by means of the law of mass action. As a chelator, furamay influence the quantity of interest, the Ca signal. On the other hand, the chelator action may be used for a number of other purposes, some of them more directly related to its molecular properties: as a chelator, competing with endogenous Ca buffers, it can be used to estimate endogenous buffers and their properties. When present at sufficiently high concentration, such that it outcompetes endogenous buffers, furareports total Ca changes and is a probe for Ca fluxes across the membrane. Here, theory and methodological considerations of such applications of furawill be summarized and results on Ca buffer and Ca flux measurements derived from various methods will be compared.