EFFECT OF HEMICHOLINIUM-3 ON TUBULAR TRANSPORT AND METABOLISM OF CHOLINE IN THE PERFUSED RAT KIDNEY

¹ Veterans Administration Hospital, Syracuse, and Department of Pharmacology and Therapeutics, Medical School, State University of New York at Buffalo, Buffalo, New York

Choline was studied in the isolated perfused rat kidney in an attempt to determine whether active tubular excretion occurred. The effect of (HC-3) was assessed to confirm other observations which suggested that HC-3 competed for choline uptake into nerves. Labeled choline and carrier choline were added to the perfusion system which recirculated through the kidney. During 70 minutes, periodic samples of urine and perfusate were analyzed for ¹⁴C-choline and its renal metabolite ¹⁴C-betaine by measurement of radioactivity associated with their respective reineckate fraction. A [(choline U/P)/ (inulin U/P) of 7.6 indicated active secretion. This ratio decreased with time as did the choline concentration in the perfusate. HC-3 was found to inhibit choline tubular transport at a molar ratio of HC-3/choline as low as 0.05. As much as 58% of the label from ¹⁴C-choline was found to be sequestered in the kidney. The label in the kidney was reduced by the presence of HC-3. The presence of HC-3 also resulted in higher perfusate choline and lower perfusate betaine.