The Journal of Neuroscience, April 1, 1999, 19(7):2609-2618
Differential Effects of Apamin- and Charybdotoxin-Sensitive
K+ Conductances on Spontaneous Discharge Patterns of
Developing Retinal Ganglion Cells
Guo-Yong
Wang,
Bruno A.
Olshausen, and
Leo M.
Chalupa
Section of Neurobiology, Physiology, and Behavior and the Center
for Neuroscience, University of California, Davis, Davis, California
95616
The spontaneous discharge patterns of developing retinal ganglion
cells are thought to play a crucial role in the refinement of early
retinofugal projections. To investigate the contributions of intrinsic
membrane properties to the spontaneous activity of developing
ganglion cells, we assessed the effects of blocking large and small
calcium-activated potassium conductances on the temporal pattern of
such discharges by means of patch-clamp recordings from the intact
retina of developing ferrets. Application of apamin and
charybdotoxin (CTX), which selectively block the small and large
calcium-activated potassium channels, respectively, resulted in
significant changes in spontaneous firings. In cells recorded from the
oldest animals [postnatal day 30 (P30)-P45], which manifested relatively sustained discharge patterns, application of either blocker
induced bursting activity. With CTX the bursts were highly periodic,
short in duration, and of high frequency. In contrast, with apamin the
interburst intervals were longer, less regular, and lower in overall
spike frequency. These differences between the effects of the two
blockers on spontaneous activity were documented by spectral analysis
of discharge patterns. Filling cells from which recordings were made
with Lucifer yellow revealed that these effects were obtained in all
three morphological classes of cells: 
, 
, and 
. These
findings provide the first evidence that apamin- and CTX-sensitive
K+ conductances can have differential effects on the
spontaneous discharge patterns of retinal ganglion cells. Remarkably,
the bursts of activity obtained after apamin application in more mature neurons appeared very similar to the spontaneous bursting patterns observed in developing neurons. These findings suggest that the maturation of calcium-activated potassium channels, particularly the
apamin-sensitive conductance, may contribute to the changes in
spontaneous firings exhibited by retinal ganglion cells during the
course of normal development.
Key words:
retinal ganglion cells; spontaneous activity; apamin; CTX; Ca-mediated K+ channels; patch-clamp
recordings; development
Copyright © 1999 Society for Neuroscience 0270-6474/99/1972609-10$05.00/0
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