Autoradiographic demonstration of the sodium-dependent high-affinity choline uptake system.

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Abstract
Mouse phrenic nerve-hemidiaphragm preparations were incubated for 10 min at 37.degree. C in an oxygenated medium containing all the constituents reported as essential for the Na dependent high-affinity choline uptake system, including [3H]-choline chloride, 3.1 Ci/mmol, 2.5 .mu.M. The phrenic nerve was stimulated by a suction electrode with square waves of 4-ms duration, 3 V, at 10 Hz. Some preparations were not stimulated. Similar preparations in which 25 .mu.M hemicholinium was included in the medium served as controls. After exposure of emulsion-coated coverslips apposed to the preparations for 53 days, development and staining of the motor endplates for acetylcholinesterase, there was a marked accumulation of Ag grains over the motor endplates of stimulated preparations. Unstimulated preparations showed considerably lighter deposits; accumulation was blocked by hemicholinium.