Sodium channels in dendrites of rat cortical pyramidal neurons.

The voltage-dependent properties that have been directly demonstrated in Purkinje cell and hippocampal pyramidal cell dendrites play an important role in the integrative capacities of these neurons. By contrast, the properties of neocortical pyramidal cell dendritic membranes have been more difficult to assess. Active dendritic conductances near sites of synaptic input would have an important effect on the input-output characteristics of these neurons. In the experiments reported here, we obtained direct evidence for the existence of voltage-dependent Na+ channels on the dendrites of neocortical neurons by using cell-attached patch and whole cell recordings from acutely isolated rat neocortical pyramidal cells. The qualitative and quantitative properties of dendritic and somatic currents were indistinguishable. Insofar as Na+ currents are concerned, the soma and primary apical dendrite can be considered as one relatively uniform compartment. Similar dendritic Na+ currents on dendrites in mature neurons would play an important role in determining the integrative properties of these cortical units.