Retinal ganglion neurons express a toxin-resistant developmentally regulated novel type of high-voltage-activated calcium channel.
1. High-voltage-activated Ca2+ currents [ICa(HVA)] were studied in immunolabeled mouse retinal ganglion neurons (RGNs) to elucidate channel-specific components and their developmental changes in vitro. 2. Neurons were dissociated at postnatal day 5. RGNs were selected for electrophysiological measurements by vital labeling with an antibody against Thy-1.2. ICa(HVA) were recorded with patch electrodes in the whole cell configuration at a holding voltage (Vh) of -90 mV. 3. A total of 111 neurons was studied. On average, 13% of ICa(HVA) was reversibly blocked by 10 microM nifedipine, approximately 30% of the compound current displayed an irreversible block by 2.5 microM omega-conotoxin (omega-CTX) GVIA. The remainder current was resistant to both drugs, suggesting that the total ICa(HVA) was a mixture of at least three different components. 4. Developmental analysis revealed a significant increase of the omega-CTX-GVIA/nifedipine-resistant component of ICa(HVA) (31% at day in vitro (DIV) 0-2, 70% at DIV 18-26) mainly at the expense of the omega-CTX-GVIA-sensitive current. No significant change was found in the nifedipine-sensitive component of ICa(HVA). 5. To characterize the Ca2+ current component that was resistant to both omega-CTX-GVIA and nifedipine at Vh -90 mV, three tests were performed. The P channel antagonist omega-agatoxin IVA (omega-Aga-IVA, 200 nM) completely failed to block ICa(HVA) in mouse RGNs. The novel Ca2+ channel blocker omega-CTX-MVIIC (5 microM) decreased the ICa(HVA) remaining after omega-CTX-GVIA treatment by only approximately 10%.(ABSTRACT TRUNCATED AT 250 WORDS)
Rothe
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Developmental Neurobiology, Max Planck Institute for Psychiatry, Martinsried, Germany.
Grantyn
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D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004351:Drug Resistance; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009498:Neurotoxins / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D013111:Spider Venoms / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009498:Neurotoxins; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D020866:omega-Conotoxin GVIA; D009543:Nifedipine