Electrophysiology of squid Schwann cells

Schwann cells are the class of glial cells of the peripheral nervous system associated with axons. The myelin-forming Schwann cells of large-diameter vertebrate axons have a clear physiological function important for axonal physiology. The squid giant axon shows a complex system for chemical signalling from axon to Schwann cell, which may be an important way for the Schwann cells to match their activity to the requirements of the axon. As the signalling involves modulation of the electrophysiological properties of the Schwann cell, a complete understanding of the signalling requires consideration of these electrical properties. The electrophysiological properties also determine the mechanisms available for ionic homeostasis of the periaxonal microenvironment. This chapter reviews current understanding of the resting and activated properties of the Schwann cell membrane, and the implications for signalling and ionic homeostasis. This survey of studies on the electrophysiology of squid Schwann cells shows a general consistency between observations in Sepioteuthis, Alloteuthis, and Loligo, good evidence for the generality of the phenomena. The documented membrane properties of the Schwann cells make for efficient periaxonal ion regulation. Further characterization of the membrane ion channels responsible for the resting and activated electrical behavior of the membranes requires rigorous study using the patch-clamp technique.