Effect of phorbol 12‐myristate 13‐acetate on Ca 2+ ‐ATPase activity in rat liver nuclei

The effect of phorbol 12‐myristate 13‐acetate (PMA) on Ca 2+ ‐ATPase activity in rat liver nuclei was investigated. Ca 2+ ‐ATPase activity was calculated by subtracting Mg 2+ ‐ATPase activity from (Ca 2+ ‐Mg 2+ )‐ATPase activity. The nuclear Ca 2+ ‐ATPase activity was significantly increased by the presence of PMA (2–20 μM) in the enzyme reaction mixture; the maximum effect was seen at 10 μM. The PMA (10 μM)‐increased Ca 2+ ‐ATPase activity was not blocked by the presence of staurosporine (2 μM) or dibucaine (2 and 10 μM), an inhibitor of protein kinase. Meanwhile, vanadate (20 and 100 μM) caused a significant reduction in the nuclear Ca 2+ ‐ATPase activity increased by PMA (10 μM). The present finding suggests that PMA has an activating effect on liver nuclear Ca 2+ ‐ATPase independent of protein kinase. © 1994 Wiley‐Liss, Inc.