title: Kv3 channels modulate calcium signals induced by fast firing patterns in the rat retinal ganglion cells.
abstract: Expression of non-inactivating Kv3.1/Kv3.2 potassium channels determines fast-spiking phenotype of many types of neurones including retinal ganglion cells (RGCs); furthermore Kv3 channels regulate neurotransmitter release from presynaptic terminals. In the present study we investigated how inhibition of Kv3 channel by low TEA concentrations modifies firing properties and Ca2+ influx in the rat RGCs. Experiments were performed on the whole-mount retinal preparations from 4 to 6 weeks old Wistar rats using simultaneous whole cell patch clamp and intracellular Ca2+ measurements in combination with single-cell RT-PCR. In response to 500-ms depolarization step the RGCs demonstrated fast firing tonic behaviour with a mean frequency of spiking 61±5 Hz (n=28). All of the tonic cells tested (n=9) expressed specific mRNA for either Kv3.1 or Kv3.2 or for both channels. Bath applications of TEA (250 μM, 500 μM and 1 mM) modified firing patterns dose-dependently as follows: firing frequency was decreased, mean action potential (AP) half-width increased and mean amplitude of after hyperpolarization was reduced. The amplitude of the Ca2+ signals induced by the cells firing was linearly dependent on number of APs with a mean slope of 7.3±0.9 nM per one AP (n=8). APs widening by TEA increased the slope of the amplitude vs. AP number plots in a dose-dependent manner: 250 μM of TEA increased the mean slope value to 9.5±1.2 nM/AP, 500 μM to 12.4±2.4 nM/AP and 1 mM to 13.2±2.9 nM/AP (n=6). All these parameters, as well as the cells firing properties, were significantly different from controls and from each other except between 500 μM and 1 mM. This is consistent with the pharmacological properties of Kv3.1/Kv3.2 channels: the TEA IC50 is in the range 150-300 μM with almost complete block at 1 mM. This suggests that Kv3.1/Kv3.2 channels underlie the fast firing of the rat RGCs and provide at a given firing frequency 1.8-fold restriction Ca2+ influx, thus protecting the cells from its cytotoxic action.
authors: Department of Neuronal Networks Physiology, Bogomoletz Institute of Physiology, Bogomoletz St, 4, 01024 Kiev, Ukraine.
authors: Kirill I
authors: KI
authors: Kuznetsov
authors: Oleksii O
authors: OO
authors: Grygorov
authors: Vitaly Yu
authors: VY
authors: Maslov
authors: Nikolay S
authors: NS
authors: Veselovsky
authors: Svetlana A
authors: SA
authors: Fedulova
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D019610:Cytoprotection / Q000502:physiology; D004983:Ethanolamines / Q000494:pharmacology; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D051670:Shaw Potassium Channels / Q000235:genetics / Q000378:metabolism*; D009435:Synaptic Transmission
chemical_list: D004983:Ethanolamines; D009467:Neuromuscular Depolarizing Agents; D051670:Shaw Potassium Channels; C009546:triethanolamine