Induction of alkaline phosphatase activity in HeLa cells by choline chloride

Choline chloride produced a dose-dependent induction of alkaline phosphatase activity in HeLa cells. At the highest concentration tested, 40 mM, there was a 5- to 7-fold increase in alkaline phosphatase activity, a significantly greater induction than that produced by equiosmolar additions of either NaCl or sucrose. Enzyme activity was higher than control values by 24 hr after the addition of the salt, although the largest increases in activity occurred between 36 and 72 hr. The induction of alkaline phosphatase activity by choline chloride could be inhibited in a dose-dependent manner by the simultaneous addition of either caffeine or theophylline. At comparable concentrations of inhibitor, the magnitude of the inhibition of the induction produced by choline chloride was greater than that observed when the xanthines were used to inhibit the induction by either 5-iodo-2'-deoxyuridine or NaCl. Choline chloride, like NaCl, produced a proportionately greater increase in the heat-stable rather than the heat-labile form of alkaline phosphatase activity.