Experimental observations on cytosolic Ca2+ oscillations
Ca2+ oscillations are among the most significant findings of the last decade in the field of intracellular signalling. Together with the mitotic oscillator, which underlies the eukaryotic cell division cycle (examined in chapter 10), Ca2+ oscillations are also one of the most important periodic phenomena uncovered in recent years in the field of biochemical and cellular oscillators. Ca2+ oscillations are of interest for a variety of reasons. First, they occur in a large number of cell types, either spontaneously or after stimulation by hormones or neurotransmitters. Second, it is by now clear that they represent the oscillatory phenomenon that is the most widespread at the cellular level, besides the rhythms encountered in electrically excitable cells. Third, Ca2+ oscillations are often associated with the propagation of Ca2+ waves within the cytosol, and sometimes between adjacent cells; even though its physiological significance remains to be determined, this phenomenon has become one of the most important examples of spatiotemporal organization at the cellular level.
Since their first direct observation in fertilized mouse oocytes (Cuthbertson & Cobbold, 1985) and hormone-stimulated hepatocytes (Woods et al., 1986,1987), which followed their earlier, theoretical prediction (Rapp & Berridge, 1977; Kuba & Takeshita, 1981) and indirect characterization (Rapp & Berridge, 1981), the number of experimental reports on Ca2+ oscillations has mushroomed at an increasing pace in recent years; these experimental results have been examined in several reviews (Berridge & Galione, 1988; Berridge, Cobbold & Cuthbertson, 1988; Berridge, 1989, 1990; Cuthbertson, 1989; Rink & Jacob, 1989; Cobbold & Cuthbertson, 1990; Jacob, 1990a; Petersen & Wakui, 1990; Tsien & Tsien, 1990; Meyer & Stryer, 1991; Tsunoda, 1991; Fewtrell, 1993) and in a special issue of Cell Calcium (Cuthbertson & Cobbold, 1991).