Permeability of the Abdominal Nerve Cord of the American Cockroach, Periplaneta Americana L. to Quaternary Ammonium Salts

Abstract

1. The influx and efflux of two series of quaternary alkylammonium cations in the abdominal nerve cord of the American cockroach have been studied. The data are interpreted as showing that increasing liposolubility tends to increase penetration, and increasing size (with respect to the smallest cross-sectional area) decreases it. 2. The influx rates of the quaternary alkylammonium cations into the cockroach central nervous system (C.N.S.) is 2-7 times lower than Na⁺ when equimolar concentrations are compared. 3. Acetylcholine penetrates into the C.N.S. rapidly due to its metabolism, since in the presence of eserine its influx rate becomes similar to that of the analogous alkylammonium cation which is unmetabolized. 4. The alkylammonium cations that penetrate into the C.N.S. appear to be distributed into fast and slow pools, as judged by their relative rates of efflux. These may represent the distribution of cations between extracellular and intracellular spaces or possibly free and bound cations in the extracellular spaces. 5. Although the alkylammonium cations penetrate the C.N.S., they apparently encounter a regulatory system that discriminates against large size, positive charge and polarity.