Calibration of Fluorescent Calcium Indicators

INTRODUCTION During the past decades, many different fluorescent indicators have been developed for measuring intracellular ion concentrations. Of particular interest are fluorescent calcium indicators because of the fundamental role of Ca2+in various cellular processes such as contraction, secretion, and gene activation. For a quantitative understanding of the physiological roles of Ca2+, fluorescence signals measured with calcium indicators have to be converted to intracellular free calcium concentration ([Ca2+]i). Similarly, changes in [Ca2+]iand the underlying calcium fluxes need to be inferred from the corresponding fluorescence changes. This article describes the theoretical background and the various principal methods for the calibration of calcium imaging data.