Electrical charge properties of connective tissue in the insect central nervous system, with regard to ionic homeostasis of the nerve cell environment.

In the central nervous system of insects, a basement membrane (the neural lamella) covers the superficial glial layer (the perineurium) and further connective tissue coats the underlying glia and neurones. The neural lamella includes proteoglycans, glycoproteins and collagen fibrils. Recent studies to investigate extracellular ion-binding show that the lamella retains little ionic lanthanum, while experiments with radioisotopes indicate elevated levels of potassium, as in many other basement membranes. The sub-perineurial interstitium is composed principally of hyaluronate. It contains discrete sites which bind lanthanum, and efflux of radioisotopes indicates that it has cation/chloride ratios to be expected for a Donnan equilibrium. Proposed effects of negative charges upon ionic homeostasis are discussed.