The Journal of General Physiology, Vol 95, 755-770, Copyright © 1990 by The Rockefeller University Press
Synaptic and voltage-gated currents in interplexiform cells of the tiger salamander retina
G Maguire, P Lukasiewicz and F Werblin
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
We have correlated the membrane properties and synaptic inputs of
interplexiform cells (IPCs) with their morphology using whole-cell
patch-clamp and Lucifer yellow staining in retinal slices. Three
morphological types were identified: (a) a bistratified IPC with descending
processes ramifying in both sublaminas a and b of the inner plexiform layer
(IPL), and an ascending process that branched in the outer plexiform layer
(OPL) and originated from the soma, (b) another bistratified IPC with
descending processes ramifying in both sublaminas a and b, and an ascending
process that branched in the OPL and originated directly from IPC processes
in the IPL, and (c) a monostratified IPC with a descending process
ramifying over large lateral extents within the most distal stratum of the
IPL, and sending an ascending process to the OPL with little branching.
Similar voltage- gated currents were measured in all three types including:
(a) a transient inward sodium current, (b) an outward potassium current,
and (c) an L-type calcium current. All cells generated multiple spikes with
frequency increasing monotonically with the magnitude of injected current.
The IPCs that send their descending processes into both sublaminas of the
IPL (bistratified) receive excitatory synaptic inputs at both light ON and
OFF that decay with a time constant of approximately 1.3 s. Slowly decaying
excitation at both ON and OFF suggests that bistratified IPCs may spike
continuously in the presence of a dynamic visual environment.
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