The effect of calcium ions and the calcium ionophore A23187 on choline uptake and phosphatidylcholine biosynthesis in chick embryo hearts

Summary The effect of increases in extracellular calcium [Ca]₀ and the calcium ionophore A23187 on choline uptake and phosphatidylcholine biosynthesis was assessed in isolated cardiac myocytes. The cells were obtained from 7-day old chick embryos and were maintained in culture. Choline uptake was examined using [methyl 3H] choline. A23187 was found to increase choline uptake through the saturable choline uptake process. Pulse chase experiments using [methyl 3H] choline showed that after a 2 h incubation with choline, about 85% of the label was recovered in phosphocholine with most of the rest in phospholipid and a small amount in CDP-choline and glycerol phosphocholine. Increases in [Ca]₀ up to 10 mM did not affect the amount of label in phosphocholine or phospholipid, the rate of disappearance of label from phosphocholine, or the rate of appearance of labelled choline in phospholipid. In contrast, A23187, at concentrations up to 10^–4 M, was associated with a significant (p<0.05) increase in choline in the phosphocholine and phospholipid pool compared to control cells. The time course of the disappearance of choline from the phosphocholine pool and appearance in phospholipid pool was not significantly different between control cells and those treated with A23187. A23187 increased choline uptake via the specific uptake process. The effect on choline uptake may be attributed to the action of A23187 to facilitate the release of calcium from specific intracellular calcium storage sites rather than a nonspecific increase in [Ca]₁ that may have resulted from the increase in [Ca]₀.Supported in part by a grant from Canadian (British Columbia) Heart Foundation