Premium
Intracellular calcium reduces light‐induced excitatory post‐synaptic responses in salamander retinal ganglion cells
Author(s) -
Akopian Abram,
Witkovsky Paul
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0043g.x
Subject(s) - depolarization , excitatory postsynaptic potential , bapta , inhibitory postsynaptic potential , cnqx , chemistry , biophysics , ampa receptor , nmda receptor , kainate receptor , membrane potential , neuroscience , biology , intracellular , receptor , biochemistry
1 The whole‐cell patch clamp technique was used to study the effect of intracellular Ca 2+ on light‐evoked EPSCs in on‐off ganglion cells in salamander retinal slices. Both AMPA and NMDA receptors contributed to the light‐evoked responses. 2 In the presence of strychnine and picrotoxin, ganglion cells responded to light onset and offset with transient inward currents at ‐70 mV. These currents were reduced by 35 ± 3 % when the light stimulus was preceded by a depolarizing step from ‐70 to 0 mV. 3 The inhibitory effect of depolarization on light‐evoked EPSCs was strongly reduced in the presence of 10 m m BAPTA. 4 The degree of EPSC inhibition by the prepulse holding potential followed the current‐voltage relationship of the Ca 2+ current found in the ganglion cell. 5 In the presence of the NMDA receptor antagonist AP‐7, glutamate‐dependent current was nearly abolished when high Ca 2+ was substituted for high Na + solution. 6 The release of Ca 2+ from internal stores by caffeine or inositol trisphosphate reduced the EPSCs by 36 ± 5 and 38 ± 11 %, respectively, and abolished the inhibitory effect of depolarization. 7 The inhibitory effect of depolarization on EPSCs was reduced 5‐fold in the presence of AP‐7, but was not reduced by the AMPA receptor antagonist CNQX. 8 Neither inhibition of Ca 2+ ‐calmodulin‐dependent enzymes, nor inhibition of protein kinase A or C had any significant effect on the depolarization‐induced inhibition of EPSCs. 9 Our data suggest that elevation of [Ca 2+ ] i , through voltage‐gated channels or by release from intracellular stores, reduced primarily the NMDA component of the light‐evoked EPSCs.