Multiple spatiotemporal patterns of dendritic Ca 2+ signals in goldfish retinal amacrine cells

Abstract

Although it has been reported that dendritic neurotransmitter releases from amacrine cells are regulated by the intracellular Ca 2+ concentration ([Ca 2+] i), their spatiotemporal patterns are not well explained. Fast Ca 2+ imagings of amacrine cells in the horizontal slice preparation of goldfish retinas under whole-cell patch-clamp recordings were undertaken to better investigate the spatiotemporal patterns of dendritic [Ca 2+] i. We found that amacrine cell dendrites showed inhomogeneous [Ca 2+] i increases in both Na + spiking cells and cells without Na + spikes. The spatiotemporal properties of inhomogeneous [Ca 2+] i increases were classified into three patterns: local, regional and global. Local [Ca 2+] i increases were observed in very discrete regions and appeared as discontinuous patches, presumably evoked by local excitatory postsynaptic potentials. Regional [Ca 2+] i increases were observed in either a single or a small number of dendrites, presumably reflecting the result of dendritic action potentials. Global [Ca 2+] i increases were observed in the entire dendrites of a cell and were mediated by Na + action potentials or multiple Na + action potentials riding on slow depolarization. Ca 2+-mediated potentials also evoked global [Ca 2+] i increase in cells without Na + spikes. These spatiotemporal dynamics of dendritic Ca 2+ signals may reflect multiple modes of synaptic integration on the dendrites of amacrine cells.