Figure 7. Dependence of the Excitatory Action of Low [Ca²⁺]_e on UNC79.

Hyperpolarizing holding currents (I_Hold, -60 pA in the neuron in panel A; -100 pA in panel B; -64.0 + 18.8 pA (wild-type), -83.7 + 19.2 pA (UNC79^-/-) and -32.7 + 17.4 pA (NALCN^-/-) for panel C) was injected to bring each neuron's steady membrane potential to -80 mV in 1.2 mM Ca²⁺-containing bath. Pulses (10 s, as illustrated in lower right in panel B) of additional depolarizing currents with increasing amplitudes (+10 to +60 pA) were injected every 50 s. (A, B) Examples of current-clamp recordings from a wild-type (A) and an UNC79 mutant neuron (B) in baths containing 1.2 mM (upper traces) or 0.1 mM (lower traces) Ca²⁺. Firing frequencies of the neurons during the 10 s depolarizing pulses are plotted in the right columns. Notice a large depolarization of holding membrane potential in the wild-type (A), but not in the mutant (B), when [Ca²⁺]_e was lowered to 0.1 mM. (C) Statistics of firing frequencies from wild-type (left), UNC79^-/- (middle) and NACLN^-/- (right) neurons. Some wild-type neurons became too depolarized in 0.1 mM Ca²⁺-containing bath to have continuous firing, presumably because of inactivation of voltage-gated ion channels. These cells were not included in the analysis in (C). See also Figure S4.