Effects of divalent cations and glucose on mitotic-like events in fused interphase-metaphase cells

The effects of Ca 2+, Mg 2+ and glucose on the mitotic-like events of prophasing and telophasing were studied in Sendai virus-fused interphase-metaphase (I-M) Chinese hamster binucleate cells. At normal extracellular ion concentrations and neutral pH, about 80–90% of I-M binucleates show prophasing (nuclear envelope dissolution and chromatin condensation) of the I nucleus and 10–15% show telophasing (nuclear envelope reformation and chromatin decondensation) of the M nucleus. To study the effects of cellular divalent cations, cells, depleted of about 77 % of exchangeable cell Ca 2+ as determined by 45Ca 2+ studies, were incubated in different concentrations of Ca 2+ or Mg 2+ for 30 min prior to cell fusion. We found that relatively high concentrations of Ca 2+ or Mg 2+ (0.84 mM) were essential for prophasing and that in the presence of 10-fold less Ca 2+ or Mg 2+ (0.084 mM) the majority of binucleates showed telophasing. In contrast to a differential effect of divalent cations on the nuclear changes, we found that glucose metabolism was required for both prophasing and telophasing. Additionally, interruption of glucose metabolism in the M cell, but not in the I cell, prior to cell fusion depressed the prophasing frequency about 70%. Although we do not know how divalent cations and glucose function in prophasing and telophasing, we will discuss evidence which suggests that the effects are not mediated through secondary effects on membrane potential, by changes in intracellular concentrations of Na + or K +, by simple osmotic changes, or through inhibition of protein synthesis.