Effects of cyclic AMP and calcium ions on virus-induced fusion of Ehrlich ascites tumor cells

Abstract

The effects of cyclic nucleotides and Ca 2+ on the fusion of Ehrlich ascites tumor cells induced by HVJ (Sendai virus) were studied. 1. 1. Addition of inhibitors of cyclic nucleotide phosphodiesterase increased the frequency of fusion up to 2 fold. None of these drugs affected the fusion and haemolysis of human erythrocytes. 2. 2. Cyclic AMP content reached a maximum (about 2 fold) after 2 min from the start of the fusion reaction and the increase in cyclic AMP was almost proportional to the dose of the virus added. 3. 3. Reagents which might increase intracellular cyclic GMP, such as insulin and carbamylcholine partially inhibited the fusion process (40% inhibition at 6 μM). 4. 4. The stimulatory effect of theophylline was dependent on the extracellular concentration of Ca 2+ with an optimal concentration of 0.5 mM. 5. 5. Theophylline partially antagonized the inhibition of the fusion reaction by cytochalasin D (0.1 μg/ml or 0.5 μg/ml). The inhibition of the fusion reaction by cytochalasin D was influenced by the extracellular concentration of Ca 2+. 6. 6. However, fusion of human erythrocytes which required neither Ca 2+ nor ATP was not affected by cyclic AMP and cytochalasin D. Therefore, fusion of Ehrlich ascites tumor cells has more complex regulatory systems than human erythrocytes. A possible mechanism of the regulation is discussed.