Uptake and metabolism of choline by the embryonic heart of the chick in vitro.

1. The uptake and metabolism of [14C]choline was investigated in isolated hearts from 4- to 14-day-old chick embryos. 2. A high-affinity uptake system of choline was present in hearts from all ages of embryos examined: the Km values were 9-11 muM, while the Vmax values ranged from 5 (14-day ventricles) to 77 (4-day atria) pmol choline/mg protein/min. 3. Hemicholinium-3, metabolic inhibitors, low temperature and low Na+ concentrations reduced the high-affinity uptake process. 4. The accumulated choline was converted mainly into phosphorylcholine in 4-day hearts, while the percentage of conversion into acetylcholine increased in older embryos.