Calcium accumulation by dendritic mitochondria declines along the apical dendrites of pyramidal neurons in area CA1 of guinea pig hippocampal slices.

An electron microscopic histochemical study was performed in stratum radiatum of area CA1 of guinea pig hippocampal slices in order to determine the spatial distribution of a dendritic mitochondrial subpopulation which accumulated calcium during in vitro incubation. A distribution gradient was found along the course of apical dendrites exhibiting the highest density values at the base of the dendrites and decaying to baseline values at about 50 microns distal from the cell body layer. The pronounced calcium accumulation by mitochondria in the proximal apical dendrites was markedly but not completely reduced by blocking L-type Ca-channels. These results (i) support the observation of a clustered distribution of L-type Ca-channels at the base of apical dendrites, (ii) designate these voltage dependent Ca2+ channels as one of the possible routes for calcium influx caused by hypoxia/ischemia induced during slice preparation, and (iii) emphasize the role of mitochondrial calcium sequestering under ischemic/hypoxic conditions.