Dendritic Ca2+ Channels Characterized by Recordings from Isolated Hippocampal Dendritic Segments

Dendritic arbors are critical for the information processing capability of central neurons, but quantitative analysis of their membrane properties has been hampered by their geometrical complexity. Here, we have focused on an important source of Ca 2+ entry in dendrites, the voltage-gated Ca 2+ channels, by applying the whole-cell voltage-clamp technique to isolated dendritic segments ("dendrosomes") from rat hippocampal neurons. We found that low voltage-activated T-type Ca 2+ channels provide a significantly larger fraction of the Ca 2+ influx in dendrites than their counterparts in cell bodies. Surprisingly, 60%–70% of the high voltage-activated Ca 2+ current in dendrosomes was N and P/Q type, and these channels were susceptible to neurotransmitter inhibition, suggesting a novel physiological role for G protein–regulated Ca 2+ channel modulation in controlling dendritic excitability and Ca 2+ signaling.