Figure 7. Voltage-Dependent Dendritic Ca²⁺ Signals.

(A) Somatic voltage step (from V _COM = −75 mV) evoked changes in somatic current (I _m) and dendritic [Ca²⁺] (single trials). Oregon-Green 488 BAPTA-1 (100 μM) signals (ΔF/F in percentages) recorded by two-photon imaging; Cs⁺-based intracellular solution.

(B) Example of spiky [Ca²⁺] transients riding on smooth responses (different cell but same protocol as in [A], single trials; some traces omitted).

(C) Ca²⁺ responses (circles) as a function of V _COM for cells lacking spiky activity; each symbol represents a single response; for each cell, amplitudes were normalized to the response-amplitude at −35 mV (see Materials and Methods); continuous line: fitted activation curve (using Equation 5).

(D) [Ca²⁺] versus voltage data before (control; black) during (purple) and after (washout; blue) bath application of CNQX (10 μM).

(E) Curve fits from C and D overlaid with fits (Equation 5) to data from the literature for P/Q-type (cyan upward triangles, g = −0.023 ± 0.001; V ₅₀ = −10.9 ± 0.5 mV; V _Slope = 4.56 ± 0.35; E _Ca = 46.8 ± 1.2 mV; [45] and R-type (orange downward triangles, g = −0.013 ± 0.003; V ₅₀ = −27.5 ± 2.1 mV; V _Slope = 8.57 ± 1.09; E _Ca = 81.2 ± 13.1 mV; [60] calcium channels, as well as for TTX-resistant Na⁺ channels (blue diamonds, g = −0.013 ± 0.0003; V ₅₀ = −26.9 ± 0.2 mV; V _Slope = 4.00 ± 0.15; E _Na = 66.2 ± 1.1 mV; [78].

(F) Somatic current as function of the step-to potential (filled circles: cell in [A], I(−75 mV) = −64 pA; open circles: cell in [B], I(−75 mV) = −86 pA).