Organic cation secretion in flounder renal tissue.

In the winter flounder, Pseudopleuronectes americanus, renal clearance experiments showed that the model organic cations, tetraethylammonium (TEA) and N'-methylnicotinamide (NMN), were strongly secreted; organic cation-to-polyethylene glycol (glomerular filtration rate marker) clearance ratios averaged 130 and 30, respectively. TEA uptake by isolated renal tubular masses was concentrative and saturable. Transport was inhibited by competitor organic cations and reduced by exposure to NaCN,2,4-dinitrophenol, ouabain, and HgCl2. Organic anions did not reduce TEA uptake. NMN was the poorest inhibitor of TEA uptake of all the organic cations tested. In addition, the rate of NMN uptake was slower than that of TEA, and the steady-state tissue-to-medium ratio was lower (5 for NMN vs. 10 for TEA; both at 25 microM). The data show the presence of an organic cation secretory system in flounder tissue that resembles the mammalian systems in several respects.