Multiple spatiotemporal patterns of dendritic Ca2+ signals in goldfish retinal amacrine cells.

Although it has been reported that dendritic neurotransmitter releases from amacrine cells are regulated by the intracellular Ca(2+) concentration (Ca(2+)), 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+). We found that amacrine cell dendrites showed inhomogeneous Ca(2+) increases in both Na(+) spiking cells and cells without Na(+) spikes. The spatiotemporal properties of inhomogeneous Ca(2+) increases were classified into three patterns: local, regional and global. Local Ca(2+) increases were observed in very discrete regions and appeared as discontinuous patches, presumably evoked by local excitatory postsynaptic potentials. Regional Ca(2+) increases were observed in either a single or a small number of dendrites, presumably reflecting the result of dendritic action potentials. Global Ca(2+) 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+) 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.