In Vitro Studies on the Uptake of 14C‐Labelled Carbamoylcholine in Mouse Kidney*)

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Abstract
Carbamoylcholine uptake by mouse kidney slices was studied. The slices were incubated in Krebs‐Ringer bicarbonate medium (37°, pH 7.4) containing 14C‐carbamoylcholine, and the 14C‐slice‐to‐medium (S/M) concentration ratio was measured. Carbamoylcholine (2μM) was rapidly accumulated in oxygen‐carbon dioxide (95:5) atmosphere, and a steady state with S/M ratio around 10 was obtained within 1/2 hr. The radioactive material extracted corresponded chromatographically to authentic carbamoylcholine. The S/M ratio was significantly reduced in the presence of metabolic inhibitors or various quaternary and tertiary amines. In nitrogen‐carbon dioxide (95:5) atmosphere the S/M ratio (2μM) reached a constant value around 1 within 1/2 hr. Incubation at 19° markedly depressed the 3 min. S/M ratio, but increased the steady state S/M ratio (1 hr). Under anaerobic conditions carbamoylcholine uptake (mmol/kg tissue; 1 hr incubation) was directly proportional to the external carbamoylcholine concentration. The aerobic uptake consisted of two components: a saturable one (maximum capacity 7 mM/kg; half saturation concentration 700 μM) and another one that increased proportionally with the external concentration. It is concluded that carbamoylcholine is taken up against a concentration gradient by a saturable, energy dependent process which is inhibited by structural analogues.