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 Ca2+ entry in dendrites, the voltage-gated Ca2+ 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 Ca2+ channels provide a significantly larger fraction of the Ca2+ influx in dendrites than their counterparts in cell bodies. Surprisingly, 60%-70% of the high voltage-activated Ca2+ current in dendrosomes was N and P/Q type, and these channels were susceptible to neurotransmittar inhibition, suggesting a novel physiological role for G protein-regulated Ca2+ channel modulation in controlling dendritic excitability and Ca2+ signaling.
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