title: The characterization of a sodium-dependent high affinity choline uptake system unassociated with acetylcholine biosynthesis.
abstract: The cardiac ganglion of the horseshoe crab, Limulus polyphemus, was incubated in Chao's solution containing 0.01 microM [3H]choline at room temperature (25 +/- 2 degrees C) and the ganglion readily accumulated the radiolabel. The ganglion uptake of [3H]choline was linear over 60 min. Kinetic analysis revealed dual choline uptake systems within the cardiac ganglion, a high affinity uptake system (Km = 2.2 microM, Vmax = 0.16 pmoles/mg/min) and a low affinity system (Km = 92.3 microM, Vmax = 3.08 pmoles/mg/min). The high affinity uptake system was sodium-dependent and inhibited by micromolar concentrations of hemicholinium-3. A 15 min pre-exposure of the ganglion to Chao's solution containing 90 mM potassium stimulated a significant increase in choline uptake. There was no detectable synthesis of [3H]acetylcholine from the [3H]choline taken up by the cardiac ganglion. The major portion of the extractable label appeared in a fraction which co-electrophoresed with phosphorylcholine. These results suggest that the sodium-dependent high affinity [3H]choline uptake system of the cardiac ganglion subserves a specific requirement for choline which is unrelated to a cholinergic function.
authors.forename: M T
authors.initials: MT
authors.lastname: Ivy
authors.forename: R
authors.initials: R
authors.lastname: Sukumar
authors.forename: J G
authors.initials: JG
authors.lastname: Townsel
mesh_terms: D000109:Acetylcholine / Q000096:biosynthesis*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002794:Choline / Q000378:metabolism*; D005260:Female; D005724:Ganglia / Q000378:metabolism*; D006329:Heart Conduction System; D006426:Hemicholinium 3 / Q000494:pharmacology; D006737:Horseshoe Crabs; D007700:Kinetics; D008297:Male; D012964:Sodium / Q000494:pharmacology*; D014316:Tritium
chemical_list: D014316:Tritium; D006426:Hemicholinium 3; D012964:Sodium; D002794:Choline; D000109:Acetylcholine