Transport of organic cations and anions by choroid plexus

Abstract

The accumulation of organic cations and anions by the isolated rabbit choroid plexus was measured and the results were considered in comparison to in vivo measurements of transport using the ventriculocisternal perfusion technique also in rabbits. The accumulation in vitro of 3H-p-aminohippurate (PAH) and 14C-N1-methylnicotinamide (NMN) was shown to be organic anion and cation specific and dependent upon oxidative metabolism since tissue/medium ratios were reduced by competitive inhibitors including dibenamine and mepiperphenidol for cation transport and probenecid for anion transport and were also reduced by cyanide and dinitrophenol. Rabbits pretreated with chlorpromazine and anesthetized with pentobarbital were perfused lateral ventricle to cisterna magna with artificial cerebrospinal fluid containing inulin, 3H-PAH and 14C-NMN. Ratios of concentrations of these substances in the perfusate to those infused were calculated. Significant reductions in the ratios for PAH and NMN compared to unulin were obtained when low rates of perfusion, 40mul/min, were employed with low concentrations of PAH (2 mug/ml) and NMN (0.2 mug/ml). Probenecid (10(-3)M) specifically increased the ratio for PAH without affecting the NMN ratios. Mepiperhenidol (10(-o) M) blocked NMN transport but no PAH. The data and calculated clearances indicate that these prototype anions and cations may be actively transported out of cerebrospinal fluid, but for cations only at a low rate.