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Electrical Properties and Anion Permeability of Doubly Rectifying Junctions in the Leech Central Nervous System
1 Department of Pharmacology, Biocenter, University of Basel, CH-4056 Basel, Switzerland
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 hyperpolarization 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 electrogenie 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.
Key words: electrical coupling, rectifying junctions, leech.
Accepted on January 28, 1988
