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The Journal of Neuroscience, May 1, 1999, 19(9):3353-3366
Ca2+-Permeable P2X Receptor Channels in Cultured
Rat Retinal Ganglion Cells
H.
Taschenberger,
R.
Jüttner, and
R.
Grantyn
Developmental Physiology, Institute for Physiology, Humboldt
University Medical School (Charité), D-10117 Berlin, Germany
ATP has been identified as an excitatory neurotransmitter in both
the CNS and peripheral nervous system; however, little is known about
the functional properties of ATP-gated channels in central neurons.
Here we used a culture preparation of the postnatal rat retina to test
the responsiveness of identified retinal ganglion cells (RGCs) and
putative amacrines to exogenous ATP and other purinoceptor agonists.
Rapidly activating ATP-induced currents (IATP) were exclusively generated in
a subpopulation (~65%) of RGCs. The latter were identified by Thy1.1
immunostaining, repetitive firing patterns, and activation of
glutamatergic autaptic currents. None of the putative amacrine cells
was ATP-sensitive. IATP could be induced
with ATP, ADP, and  , -mATP but not with adenosine. It was
antagonized by suramin. The current-voltage relationship of
IATP showed marked inward rectification.
Dose-response analysis yielded an EC50 of 14.5 µM, with a Hill coefficient of 0.9. Noise analysis of
IATP suggested a mean single channel
conductance of 2.3 pS. Retinal P2X purinoceptor channels exhibited a
high permeability for Ca2+.
PCa/PCs obtained from reversal
potentials of IATP under bi-ionic conditions
amounted to 2.2 ± 0.7. In the majority of cells, the decay of
IATP was biphasic. The degree of current
inactivation during the first 2 sec of agonist application was highly
variable. Heterogeneity was also found with respect to the sensitivity
to ADP and ,-mATP and the blocking action of suramin, suggesting expression of multiple P2X receptor subtypes. Our results indicate that
activation of P2X receptor channels represents an important pathway for
Ca2+ influx in postnatal RGCs.
Key words:
adenosine triphosphate; purinoceptors; P2X; rat; retina; retinal ganglion cells; patch clamp; Ca2+
permeability; fura-2
Copyright © 1999 Society for Neuroscience 0270-6474/99/1993353-14$05.00/0
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