ROLE OF CALCIUM-CHANNEL SUBTYPES IN CALCIUM TRANSIENTS IN HIPPOCAMPALCA3 NEURONS

Multiple subtypes of voltage-gated calcium channels are differentially localized in brain neurons suggesting that they serve distinct roles in neuronal excitation and signaling. In organotypic hippocampal slice cultures, class D (L-type) calcium channels are predominantly located in the cell bodies of CA3 neurons while class B (N-type) and class A (P or Q-type) are localized in dendrites and associated presynaptic te rminals with relatively low somal expression. Using specific antagonis ts to inhibit calcium transients recorded in CA3 neuronal cell bodies, we found that L-type calcium channels have a predominant role in soma l calcium transients elicited by trains of strong stimuli applied to e ither the soma or the distal apical dendrite while class A calcium cha nnels make a smaller contribution. Presynaptic class B (N-type) and cl ass A (P- and/or Q-type) calcium channels are critical for glutamate-m ediated synaptic transmission onto the dendrites of CA3 neurons. Posts ynaptic class A and B calcium channels detected on the dendritic shaft by immunocytochemistry were not found to contribute substantially to somal calcium transients during repetitive stimulation of distal dendr ites, but sodium channels were required for calcium transients elicite d by somatic or dendritic stimulation. Our results show that the diffe rent calcium channel subtypes serve distinct roles in cellular activat ion and transmission of signals in CA3 neurons, consistent with their differential subcellular localization.