ELECTRICAL PROPERTIES AND ANION PERMEABILITY OF DOUBLY RECTIFYING JUNCTIONS IN THE LEECH CENTRAL NERVOUS SYSTEM

A study has been made of the electrical connections between touch sensory (T) neurones in the leech central nervous system (CNS) which display remarkable double rectification: depolarization spreads in both directions although hyper-polarization spreads poorly. Tests were made to determine whether this double rectification was a property of the junctions themselves or whether it resulted from changes in the length constants of processes intervening between the cell body and the junctions. Following trains of action potentials, T cells and their fine processes within the neuropile became hyperpolarized through the activity of an electro-genie sodium pump. When any T cell was hyperpolarized by 25 mV by repetitive stimulation, hyperpolarization failed to spread to the T cells to which it was electrically coupled. Further evidence for double rectification of junctions linking T cells was provided by experiments in which Cl ~ was injected electrophoretically. Cl ~ injection into one T cell caused inhibitory potentials recorded in it to become reversed. After a delay, Cl ~ spread to reverse IPSPs in the coupled T cell. Movement of Cl~, like current flow, was dependent on membrane potential. When the T cell into which Cl ~ was injected was kept hyperpolarized, Cl ~ failed to move into the adjacent T cell. Upon release of the hyperpolarization in the injected T cell, Cl ~ moved and reversed IPSPs in the coupled T cell. Together these results indicate that the gating properties of channels linking T cells are voltage-dependent, such that depolarization of either cell allows channels to open whereas hyperpolarization causes them to close