Measuring Cytoplasmic Calcium: A Review of Three Methods With Emphasis on the Practical Aspects of Their Use

We have used the three major techniques for measuring cytoplasmic calcium concentration to quantify calcium changes in a variety of cells during a number of developmental processes. In this paper, we describe our experiences with aequorin, calcium electrodes, and fluorescent calcium indicators. The Xenopus oocyte is used as the prime example throughout this discussion, as we have done all three types of measurements in oocytes. Although each of these methods gives roughly the same value for the cytoplasmic calcium concentration in oocytes, each method has its own advantages and disadvantages when it comes to practical experiments. The particular problems with each of the methods are discussed in detail. We conclude that the choice of method depends on the type of information that is required. Calcium electrodes are probably the most precise method but are also the most technically difficult and only provide very localized measurements. Aequorin is quite suitable when an overall average of calcium levels in a cell is required but it is difficult to get good information on the spatial distribution of calcium. Fluorescent indicators are the most straightforward method to use and provide much information about the spatial distribution of calcium in cells as well as average levels in cell suspensions, however they are the most difficult to calibrate.