Figure 1. CDI of neuronal L-type Ca²⁺ channels requires AKAP79/150-anchored PKA.

(A) (Left) Top three images, fluorescence images of cultured rat neurons transfected with 150RNAi and: wild-type AKAP79 (79wt), AKAP79ΔPKA (79ΔPKA), or AKAP79Pro2 (79Pro2). Bottom three images, differential interference contrast images of short-term cultured neurons from wild-type mice, AKAP150ΔPKA mice and AKAP150–/– mice. (Center) Superimposed, normalized records of pharmacologically-isolated L-channel Ca²⁺ (red) or Ba²⁺ (black) currents. (Right) Mean inactivation rates (1/τ). Number of cells recorded per condition (n) is noted on each bar.

(B) CDI index, calculated as the difference between r₄₀₀ in Ba²⁺ and r₄₀₀ in Ca²⁺. Black bars represent knockdown/replacement experiments in rat neurons and gray bars represent knockin mice, in all four panels. Fractional depression of divalent charge influx as a consequence of CDI, calculated as the difference between peak-normalized Ba²⁺ charge influx and peak-normalized Ca²⁺ charge influx during 500 ms depolarizations.

(C) Peak Ca²⁺ current density and Ca²⁺ charge density for each of the experimental manipulations in B. Dividing peak Ca²⁺ current (I_Ca, pA) by a measure of membrane surface area, cell capacitance (C_m, pF), yields the density of Ca²⁺ current (pA/pF). Ca²⁺ charge density (pC/pF) was calculated as the integrated Ca²⁺ current during 500-ms depolarization (pC) divided by cell capacitance (pF).

(D) For 150RNAi-transfected rat neurons, voltage-dependence of Ca²⁺ current density for 79wt (●) or 79ΔPKA (▲) co-transfected neurons, compared with the voltage-dependence of inactivation rate for Ca²⁺ current, for 79wt (○) or 79ΔPKA (△) co-transfected neurons. Error bars indicate standard error of the mean. Mean values were compared using ANOVA with a posthoc Bonferroni correction. Statistical significance marked as * p = 0.05, **p = 0.01, *** p = 0.005, and **** p = 0.001.