Ca2+-permeable P2X receptor channels in cultured rat retinal ganglion cells.
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 (approximately 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 alpha,beta-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 microM, 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 alpha,beta-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.
Taschenberger
H
H
Developmental Physiology, Institute for Physiology, Humboldt University Medical School (Charité), D-10117 Berlin, Germany.
Jüttner
R
R
Grantyn
R
R
D000241:Adenosine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D012044:Regression Analysis; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013498:Suramin / Q000494:pharmacology
D018048:Receptors, Purinergic P2; D013498:Suramin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000241:Adenosine; D002118:Calcium