Extracellular ionic concentrations in Bombyx mori L. central nervous system

Aim of this study was to determine the ionic concentration gradients at the cellular membrane level in the central nervous system of an insect where the haemolymphatic sodium concentration relative to that of potassium is too low to allow action potential generation. The intracellular ionic concentrations determined by electrophysiological experiments performed at different Na and K concentrations in the perfusing solution, the Na and K concentrations in the nerve cord tissue water, and the extracellular spaces observed by electron microscopy, support the conclusion that the cells in the ventral nerve cord of Bombyx mori function in a medium with a relatively low potassium content and a high sodium concentration. This fluid is in a microenvironment protected by a barrier, the perineurium and associated glial elements, where must be located a regulation mechanism of cation composition. In order to aid the microelectrode penetration the preparations were exposed to Pronase. The Pronase action was investigated by electron microscopy and determinations of ionic concentrations.