Carrier-Mediated Transport of Tetramethyl and Tetraethylammoniums in Isolated Rat Hepatocytes

The uptake mechanism of tetramethylammonium (TMA) and tetraethylammonium (TEA) ions was investigated using the isolated rat hepatocytes. TMA and TEA were trans ported against concentration gradient into the isolated hepatocytes. The cellular uptake of TMA and TEA was inhibited by their structural analogs and metabolic inhibitors, and was also temperature-dependent. The uptake of these compounds showed saturation with in creasing extracellular concentration. Thiamine, the endogenous quaternary ammonium, and hemicholinium-3 markedly inhibited the cellular uptake of TMA and TEA. The inhibition by choline was moderate. The mode of uptake inhibition by thiamine and choline was the competitive type of inhibition. These results suggested that TMA and TEA are trans ported into the hepatocytes by the common carrier system same as most likely that for thiamine.