Single-Cell and Subcellular Measurement of Intracellular Ca2+ Concentration

Measurement of the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) in populations of cells is an excellent tool to complement population measurements of other cell parameters, but the usefulness of this approach is limited by several problems, not the least of which is temporal averaging. In population studies, agonists often evoke a characteristic peak and plateau type of response irrespective of the stimulus intensity. However, equivalent experiments using single cells can often reveal exceedingly complex patterns, such as oscillations of the cytosolic Ca²⁺ concentration ([Ca²⁺ ]_c ) (1 ). By and large these patterns cannot be observed in population studies since cells oscillate out of phase and at different frequencies, resulting in a smooth population average. It is only when cells are electrically well coupled that synchronized, population oscillations can be recorded, but this case is more the exception than the rule.