This review updates the imaging of free cytosolic calcium with the chemilum
inescent aequorins. Basic principles of chemiluminescence are discussed and
the biochemistry of aequorins is briefly described. The review provides pr
actical tips on handling and microinjecting aequorins and describes availab
le ultra low light imaging systems. It is argued that aequorin-based calciu
m imaging is the method of choice for exploratory studies, since it is extr
emely sensitive, can detect a broad range of calcium concentrations, and al
lows for continuous recording during long periods of time. However, fluores
cent methods are needed to attain high spatial resolution. (C) 1999 Wiley-L
iss, Inc.