Figure 3.

Stimulation of IP synthesis by released nucleotides. After loading with myo-[³H]inositol and preincubation in LiCl (10 mm), the cells were incubated for 30 min in LiCl alone or LiCl plus the indicated concentrations of apyrase, ATP, bradykinin (Bk), KCl (NaCl was reduced accordingly), or CdCl₂. The amount of radioactivity retrieved within the fraction of inositol monophosphate (IP₁) was calculated as percentage of the total water-soluble radioactivity extracted from the cell cultures, and values obtained in the presence of the above agents were normalized to the data obtained in their absence (normalized to basal); n = 5-14. ^**p < 0.01 versus the value obtained in the presence of LiCl only; ⁺⁺p < 0.01 versus the value obtained in the presence of LiCl plus ATP; ^##p < 0.01 versus the value obtained in the presence of LiCl plus 100 mm K⁺. In the presence of LiCl only, 2968.6 ± 200.5 cpm were retrieved in the IP₁ fraction (n = 16).