Activation of nuclear calcium dynamics by synaptic stimulation in cultured cortical neurons.
L-type voltage-sensitive Ca2+ channels (VSCCs) are enriched on the neuronal soma and trigger gene expression during synaptic activity. To understand better how these channels regulate somatic and nuclear Ca2+ dynamics, we have investigated Ca2+ influx through L-type VSCCs following synaptic stimulation, using the long-wavelength Ca2+ indicator fluo-3 combined with laser scanning confocal microscopy. Single synaptic stimuli resulted in rapid Ca2+ transients in somatic cytoplasmic compartments (<5 ms rise time). Nuclear Ca2+ elevations lagged behind cytoplasmic levels by approximately 60 ms, consistent with a dependence on diffusion from a cytoplasmic source. Pharmacological experiments indicated that L-type VSCCs mediated approximately 50% of the nuclear and somatic (cytoplasmic) Ca2+ elevation in response to strong synaptic stimulation. In contrast, relatively weak excitatory postsynaptic potentials (EPSPs; approximately 15 mV) or single action potentials were much less effective at activating L-type VSCCs. Antagonist experiments indicated that activation of the NMDA-type glutamate receptor leads to a long-lasting somatic depolarization necessary to activate L-type VSCCs effectively during synaptic stimuli. Simulation of action potential and somatic EPSP depolarization using voltage-clamp pulses indicated that nuclear Ca2+ transients mediated by L-type VSCCs were produced by sustained depolarization positive to -25 mV. In the absence of synaptic stimulation, action potential stimulation alone led to elevations in nuclear Ca2+ mediated by predominantly non-L-type VSCCs. Our results suggest that action potentials, in combination with long-lived synaptic depolarizations, facilitate the activation of L-type VSCCs. This activity elevates somatic Ca2+ levels that spread to the nucleus.
Nakazawa
H
H
Department of Psychiatry, University of British Columbia, Vancouver, Canada.
Murphy
T H
TH
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D020746:Calcium Channels, L-Type; D002467:Cell Nucleus / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D007700:Kinetics; D018613:Microscopy, Confocal; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000502:physiology*
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D016194:Receptors, N-Methyl-D-Aspartate; D002118:Calcium