Abstract
Extracellular Ca2+ has been demonstrated to be required for proliferation of a wide variety of nonneoplastic cells of mesenchymal and epithelial origin bothin vivoandin vitro(Boyntonet al., 1974,1981; Boynton and Whitfield, 1976; Henningset al., 1980; Swierengaet al., 1980; Lechner and Kaighn, 1981; Swierenga, 1984). Specific stages of the growth-division cycle require extracellular Ca2+ as well as intracellular Ca2+ transients (Boynton et al., 1985a; Hazeltonet al., 1979; Heskethet al., 1987). Neoplastic cells, on the other hand, require 10-to 50-fold less extracellular Ca2+ than their neoplastic counterparts for their proliferative activity regardless of the means of neoplastic transformation (Swierengaet al., 1980; Boyntonet al., 1981; Whitfieldet al., 1987). However, it is not known if neoplastic cells require intracellular Ca2+ transients for cell cycle progression. It was first demonstrated in 1965 that adenovirus-infected cells could be selected from uninfected cells by culturing them in Ca2+ -deficient medium (Freemanet al., 1965, 1966). Balket al. (1973) extended this observation in 1973 to Rous sarcoma virus-infected chicken fibroblasts, and Boynton and Whitfield (1976) found that neoplastic cells transformed by DNA or RNA viruses, by chemicals, or by spontaneous means all required 10-to 50-fold less extracellular Ca2+ for proliferative activity.