Renal tubular excretion of triethylcholine (TEC) in the chicken: enhancement and inhibition of renal excretion of choline and acetylcholine by TEC.

1. [3H]-triethylcholine (TEC) was actively transported by the renal tubule of the chicken at a rate 85% that of simultaneously administered p-aminohippuric acid (PAH). 2. TEC was demonstrated to be transported by the organic cation transport system in the kidney through inhibition with quinine and the bio-cation choline. 3. When the infusion of TEC was increased to 2 times 10(-6) mol kg(-1) min(-1) reaching the infused kidney, the transport of [3H]-TEC was inhibited, suggesting that an excretory transport maximum for TEC in the renal tubules had been reached. 4. The excretion of both choline and acetylcholine was enhanced by TEC loads as low as 1 times 10(-18) mol kg(-1) min(-1). Enhancement continued as TEC infusion was increased up to approximately 1 times 10(-7) mol kg(-1) min(-1) at which point this enhancement was converted to inhibition. 5. Possible mechanisms for the biphasic effect of TEC on organic cation transport are discussed.