Subthreshold synaptic activation of voltage-gated Ca2+ channels mediates a localized Ca2+ influx into the dendrites of hippocampal pyramidal neurons.
1. Whole cell recordings and high-speed fluorescence imaging were used to investigate the spatial and temporal characteristics of Ca2+ influx during synaptic activity in hippocampal CA1 pyramidal neurons. Brief, subthreshold trains of synaptic potentials elicited by Schaffer collateral stimulation produced transient increases in [Ca2+]i in the apical dendrites near the site of synaptic input. The rises in [Ca2+]i were not due to Ca2+ entry through N-methyl-D-aspartate (NMDA)-activated or non-NMDA-activated glutamate channels, but were reduced by low concentrations of Ni2+. Hyperpolarizing prepulses caused an increase in the synaptically evoked Ca2+ transients, whereas strong hyperpolarization during the train prevented the rise in [Ca2+]i. The data suggest that subthreshold synaptic activity can open low-voltage-activated (T-type) Ca2+ channels and produce a local increase in intradendritic [Ca2+]. Such local increases in [Ca2+]i may be important for modulating the strength of synaptic connections.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D003712:Dendrites / Q000502:physiology*; D005453:Fluorescence; D006624:Hippocampus / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology
D015220:Calcium Channels; D002118:Calcium