Fig. 1

Mg²⁺-activated ecto-nucleotidase activity in the presence of ATP (1 mM). a Measurement of nucleotidase activity in the presence of 3 mM MgSO₄ (Mg²⁺) and absence of both NaCl and KCl (Na⁺, K⁺) in HepG2 cells. EDTA (10 mM) strongly inhibited the Mg²⁺-activated ATPase activity. n = 4. b Measurement of nucleotidase activity in the presence of 3 mM MgSO₄, 120 mM NaCl and 15 mM KCl in HepG2 cells. Inhibition by ouabain (100 μM) of the (Mg²⁺, Na⁺, K⁺)-activated ATPase activity was slight but significant. n = 7. c Ecto-nucleotidase activity was calculated as the difference between the activities in the presence and absence of 10 mM EDTA. Na⁺,K⁺-ATPase activity was calculated as the difference between the activities in the presence and absence of 100 μM ouabain. Ecto-nucleotidase activity was about three times greater than Na⁺,K⁺-ATPase activity in HepG2 cells. d Ecto-nucleotidase activity was measured at pH 5–9. n = 4. e Ecto-nucleotidase activity was measured at pH 7.4 and pH 9 in the presence (+) and absence (−) of 100 μM of levamisole, an inhibitor of alkaline phosphatase. **Significantly different (p < 0.01). NS not significant (p > 0.05). n = 4