FAST IMAGING OF [CA](I) REVEALS PRESENCE OF VOLTAGE-GATED CALCIUM CHANNELS IN DENDRITIC SPINES OF CULTURED HIPPOCAMPAL-NEURONS

1 Cultured hippocampal neurons were recorded with a patch pipette cont aining 100 mu M of the calcium indicator Fluo-3, and one of their dend rites, carrying dendritic spines, was visualized with a x 100, 1.3-num erical aperture oil objective. Calcium spikes evoked by depolarizing t he somata and changes in free dendrite and spine calcium concentration s ([Ca](d) and [Ca](s), respectively) were monitored with a cooled cha rge-coupled device (CCD) camera, acquiring images at a rate of 17-20 m s per frame. In the majority of spine-dendrite pairs, [Ca](s) rose fas ter and to a higher level than the adjacent [Ca](d). Likewise, topical application of glutamate evoked a faster and larger change in [Ca](s) than in [Ca](d). The rise of intracellular calcium concentration in r esponse to a depolarizing current pulse, but not in response to glutam ate, was reduced in the presence of the calcium antagonist verapamil i n both dendrites and spines. It is suggested that dendritic spines pos sess voltage-gated calcium channels.