Measurements of the free calcium concentration of single quiescent human fibroblasts before and after serum addition.

We have developed the technique for injecting aequorin into cells so that it is now possible to measure the free calcium concentration of single mammalian somatic cells. Using this method, the free calcium concentration of serum-starved quiescent human fibroblasts was determined to be 3.3 x 10(-7) M. After feeding the cells with serum a significant increase in free calcium was observed in some cells. The exact cause of such an increase is unclear but it may indicate that a large increase in free calcium is an important event in the stimulation of cell growth.