Potassium Ions and Insect Nerve Muscle

The ionic composition of the blood of insects, unlike that of vertebrates and most other invertebrates, shows a wide range of values, especially in regard to the physiologically important ions of sodium and potassium. Preparations are described in which the effect of potassium on the active nerve and muscle properties of Locusta migratoria have been investigated. The nerve axons are depolarized by high concentrations of potassium ions in the same way as vertebrate and crustacean axons. The whole nervous system is surrounded by a sheath which is an effective barrier to the diffusion of potassium ions. The muscle-fibre membrane is also depolarized by high concentrations of potassium ions in a similar way to muscle-fibre membranes of other animals which have been previously investigated. The tracheolated membranes surrounding the muscles, and the close arrangement of the constituent fibres, delay the passage of potassium ions through the muscles. It is predicted that the mechanical properties of the muscles of a herbivorous insect will be found to be subject to fairly marked changes if the blood potassium rises or falls to an appreciable extent.