A simple method for incorporating aequorin into mammalian cells.

A simple method for incorporating aequorin into mammalian cells to measure cytosolic ionized Ca2+ is described and compared with scrape loading and hypoosmotic treatment (HOST). The procedure consists of incubating the cells for 10 min and centrifuging them at 200 g for 30 s in the presence of aequorin. This method incorporates the same amount of photoprotein as scrape loading but 70% less than HOST. Cytosolic ionized Ca2+ has been measured in hepatocytes, kidney cells and tubules, macrophages, and cardiac myocytes loaded with aequorin by this new procedure.