Figure 8.
Calcium dynamics during resting activity in RD RGCs. A, Simultaneously recorded calcium indicator fluorescence (Ca2+, red) and membrane potential (Vm, black) from cells show at left. Red boxes on proximal dendrites indicate scanned regions. B, Ca2+ signals (red) and spike rate (black; bin width, 150 ms) during resting activity [injected current (Iinj) = 0] from two different cells than in A. Note the longer time scale. In the ON cell (left), Iinj reduced spike rate and resting Ca2+. Baseline membrane potentials for the ON cell at rest (during pulse) were −71, −70 (−94), and −70 (−108) mV for top, middle, and bottom panels, respectively. Baseline membrane potentials for the OFF-T cell at rest during pulse were −70, −70 (−87), −70 (−95) mV for top, middle, and bottom panels, respectively. C, Blow-ups of regions corresponding to bars in B (middle, ∼t = 9 s for ON cell; bottom, ∼t = 7 s for OFF-T cell). Note that both spikes and subthreshold regenerative-like events are associated with Ca2+ signals during hyperpolarization in OFF-T cell (arrows). The bottom right plot shows rebound-evoked Ca2+ signal during resting activity (Iinj = −400 pA for 0.5 s). The superimposed gray trace is the mean of three responses to −550, −400, and −300 pA. The hyperpolarizing portion of the mean response is shown in the inset on the right to emphasize Ca2+ decrease. Scale bars: A, 25 μm; C, inset, 10% ΔF/F.