Figure 6.
Voltage dependence of calcium transients develops rapidly. In all panels, thick traces mark hyperpolarization to approximately -90 mV, and thin traces depolarization to approximately -50 mV. Before the prepulse, cells were held at approximately -70 mV. A, Depolarizing versus hyperpolarizing 500 msec prepulses lead to a pronounced difference in (ΔF/F)AP amplitudes. The traces from a representative experiment show the injected current (top, schematic), the recorded somatic voltage (middle), and the respective calcium transients (bottom). B, Voltage dependence evolves with a time constant of ∼300 msec. Cumulative data from all experiments. Average data are plotted as ratios of transient amplitudes for depolarization and hyperpolarization, RD/H, versus duration of the polarization interval (100, 250, 500, and 1000 msec). Data are shown ± SD. The dotted line corresponds to a single exponential fit (τ = 290 msec). C, Close-to-spiking-threshold depolarization results in considerable calcium influx. Dashed traces mark strong depolarization. Again, the polarization interval was 500 msec. Note the characteristic hump in the dashed voltage recording.