[Progress and problems in measuring the [Ca2+]i]

Since Ca(2+) has been recognized as an important intracellular second messenger for many signal transduction pathways, several methods to measure the intracellular Ca(2+) concentration ( [Ca(2+)](i) ) have been invented, including Ca(2+) microelectrodes, Ca(2+) sensitive dyes, and artificial Ca(2+) sensitive proteins. These techniques have been further evolving in combination with progression of computer technology, while true [Ca(2+)](i) is not still measurable.