Calcium transients in dendrites of neocortical neurons evoked by single subthreshold excitatory postsynaptic potentials via low-voltage-activated calcium channels.
Simultaneous recordings of membrane voltage and concentration of intracellular Ca2+ ([Ca2+]i) were made in apical dendrites of layer 5 pyramidal cells of rat neocortex after filling dendrites with the fluorescent Ca2+ indicator Calcium Green-1. Subthreshold excitatory postsynaptic potentials (EP-SPs), mediated by the activation of glutamate receptor channels, caused a brief increase in dendritic [Ca2+]i. This rise in dendritic [Ca2+]i was mediated by the opening of low-voltage-activated Ca2+ channels in the dendritic membrane. The results provide direct evidence that dendrites do not function as passive cables even at low-frequency synaptic activity; rather, a single subthreshold EPSP changes the dendritic membrane conductance by opening Ca2+ channels and generating a [Ca2+]i transient that may propagate towards the soma. The activation of these Ca2+ channels at a low-voltage threshold is likely to influence the way in which dendritic EPSPs contribute to the electrical activity of the neuron.
Markram
H
H
Max-Planck-Institut für Medizinische Forschung, Abteilung Zellphysiologie, Heidelberg, Germany.
Sakmann
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism*; D004056:Differential Threshold; D008564:Membrane Potentials; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013569:Synapses / Q000502:physiology*
D015220:Calcium Channels; D018091:Receptors, AMPA; D002118:Calcium