A method for recording intracellular [Ca2+] transients in cardiac myocytes using calcium green-2

Calcium green-2 (Ca green) is a non-ratiometric fluorescent Ca2+ indicator with an affinity for Ca2+ (dissociation constant Kd = 3 microM) that is lower than more commonly used indicators such as fura-2 and fluo-3. This low Ca2+ affinity, coupled with a high quantum yield, allows cells to be loaded with low concentrations of Ca green, avoiding problems of cytosolic Ca2+ buffering and a low signal-to-noise ratio. This communication presents a method for monitoring intracellular [Ca2+] changes in isolated rat ventricular myocytes loaded with Ca green and the fluorescent pH indicator carboxy SNARF-1 (SNARF). SNARF provides a Ca(2+)-insensitive signal with which Ca green fluorescence can be corrected for cell motion and dye-loading artifacts.