Figure 2.

CREB signal strength is a steep function of membrane potential and channel activity. (A) SCG neuron under current clamp in TTX. In 4 mM K⁺, the cell rested at −60 mV. Exposure to [K⁺] as indicated caused stepwise depolarizations. (B) Membrane potential plotted against [K⁺]_o. Slope of linear fit is 58.1 mV per 10-fold change in [K⁺]_o. (C) CREB signal strength, measured as in Fig. 1 E and in Materials and methods (five to eight experiments), plotted against voltage. 100% is the full change in pCREB from baseline to maximal levels. Linear fit shows that signal strength is steeply voltage dependent, as if governed by a gating particle with valence (z) between 4 and 5. (D) Voltage-clamp recordings with 2-mM Ca²⁺ Tyrode's as bathing solution. Pulse depolarizations to the voltages indicated. Traces are the mean of ten consecutive sweeps at each voltage. (E) Ca²⁺ flux (▪; as in D) and signal strength (○) plotted versus membrane potential. Solid lines are single exponential fits. Dashed lines indicate the voltages generated by each [K⁺]_o (n = 5–8 experiments). Error bars represent SEM.