T-type calcium channels mediate the transition between tonic and phasic firing in thalamic neurons.
Thalamic neurons undergo a shift from tonic to phasic (burst) firing upon hyperpolarization. This state transition results from deinactivation of a regenerative depolarizing event referred to as the low-threshold spike. Isolated adult guinea pig thalamic (dorsal lateral geniculate) neurons exhibited low-threshold spikes that could be blocked by low concentrations of nickel but were unaffected by the dihydropyridine nimodipine. Whole-cell voltage-clamp recordings from these cells demonstrated a low-threshold, rapidly inactivating (T) Ca2+ current that manifested similar voltage dependency and time course as the low-threshold spike. Like low-threshold spikes, the T-type Ca2+ current was eliminated by nickel but was unaffected by nimodipine. In thalamic neurons, T-type Ca2+ channels underlie the low-threshold spike and, therefore, play a critical role in regulating the firing pattern of these cells.
Suzuki
S
S
Medical Neurology Branch, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892.
Rogawski
M A
MA
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D005829:Geniculate Bodies / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009474:Neurons / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D015220:Calcium Channels; D013779:Tetrodotoxin; D009553:Nimodipine; D009532:Nickel