Voltage-gated calcium channels mediate intracellular calcium increase in weaver dopaminergic neurons during stimulation of D2 and GABAB receptors.
The weaver (wv) mutation affects the pore-forming region of the inwardly rectifying potassium channel (GIRK) leading to degeneration of cerebellar granule and midbrain dopaminergic neurons. The mutated channel (wvGIRK) loses its potassium selectivity, allowing sodium (Na+) and possibly calcium ions (Ca2+) to enter the cell. Here we performed whole cell patch-clamp recordings combined with microfluorometry to investigate possible differences in calcium ([Ca2+]i) dynamics in native dopaminergic neurons (expressing the wvGIRK2 subunits) in the midbrain slice preparation from homozygous weaver (wv/wv) and control (+/+) mice. Under resting conditions, [Ca2+]i was similar in wv/wv compared with +/+ neurons. Activation of wvGIRK2 channels by D2 and GABAB receptors increased [Ca2+]i in wv/wv neurons, whereas activation of wild-type channels decreased [Ca2+]i in +/+ neurons. The calcium rise in wv/wv neurons was abolished by antagonists of the voltage-gated calcium channels (VGCC); voltage clamp of the neuron at -60 mV; and hyperpolarization of the neuron to -80 mV or more, in current clamp, and was unaffected by TTX. Therefore we propose that wvGIRK2 channels in native dopamine neurons are not permeable to Ca2+, and when activated by D2 and GABAB receptors they mediate membrane depolarization and an indirect Ca2+ influx through VGCC rather than via wvGIRK2 channels. Such calcium influx may be the trigger for calcium-mediated excitotoxicity, responsible for selective neuronal death in weaver mice.
Guatteo
Ezia
E
Laboratory of Experimental Neurology, Fondazione Santa Lucia Istituto di Ricovero e Cura a Carattere Scientifico, 00179 Rome, Italy.
Bengtson
C Peter
CP
Bernardi
Giorgio
G
Mercuri
Nicola B
NB
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D004298:Dopamine / Q000494:pharmacology / Q000502:physiology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D018755:GABA Agonists / Q000494:pharmacology; D006720:Homozygote; D008636:Mesencephalon / Q000166:cytology / Q000502:physiology; D051379:Mice; D008818:Mice, Neurologic Mutants; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000378:metabolism; D017448:Receptors, Dopamine D2 / Q000502:physiology*; D018080:Receptors, GABA-B / Q000502:physiology*
D015220:Calcium Channels; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D018755:GABA Agonists; C497069:Kcnj6 protein, mouse; D024661:Potassium Channels, Inwardly Rectifying; D017448:Receptors, Dopamine D2; D018080:Receptors, GABA-B; D001418:Baclofen; D002118:Calcium; D004298:Dopamine