IN VITRO BIOELECTRIC POTENTIALS OF CHOROID PLEXUS IN FOURTH VENTRICLE OF CATS AND RABBITS

The choroid plexus of the 4th ventricle was punctured in vivo in anesthetized cats, using Ag/AgCl/KCl electrodes (minimum diameter 20 μ). Mean potential difference against CSF was -6,1 mV. In addition, choroid plexus was removed from living animals (cats, rabbits) and punctured with Ling-Gerard electrodes (diameter <1-2 μ) after exposure to mock CSF equilibrated with CO2. Rapidly decreasing potentials could be distinguished from constant potentials. The latter can be regarded as transependymal potentials (TEP). The mean value when measured against CSF was -3,3 mV. Variation of CSF toward alkalinity was followed by a weak depolarization, acid CSF pH caused hyperpolarization of TEP. A decrease in Na+ concentration regularly caused a depolarization, regardless wether the lacking ions were replaced by K+ or by choline ions in equivalent amounts. When 10 μg/ml of ouabain were added to the mock CSF there was a reduction in TEP which could be reversed by replacing choline chloride for NaCl. It is concluded that TEP develops autonomously in the isolated plexus; the ependymal structures are thought to participate in the generation of potential differences between blood and CSF, as have been described by various authors. © 1969 Springer-Verlag.