Figure 7.

Ca_v1 currents and cell surface Ca_v1.2 protein levels are reduced in cortical neurons from densin KO mice. A, I_Ba was evoked by voltage ramps from −60 to +80 mV (0.5 ms/mV) from a holding voltage of −60 mV in cortical neurons from WT (n = 8 cells from 3 mice) and densin KO (n = 8 from 3 mice) mice before (−isr) and after (+isr) bath application of isradipine (5 μm). B, Measurement of the Ca_v1-mediated current. Left, Peak currents for data collected as in A were plotted for voltage ramps evoked every minute before and after application of isradipine. Right, Fractional Ca_v1 current represents the fraction of the total I_Ba that was blocked by isradipine. Statistical significance was determined by Student's t test. C, Biotinylated cell surface proteins in prefrontal cortex of WT and densin KO mice were isolated on streptavidin agarose and subjected to Western blotting. Left, Representative Western blot probed with antibodies against Ca_v1.2, Na⁺/K⁺ ATPase, and GAPDH. Lanes represent biotinylated proteins before (input; ∼10% of total amount used for pull-down) or after streptavidin pull-down (surface). Results are representative of four independent experiments, with one WT and one densin KO littermate used per experiment. Right, Densitometric analysis of biotinylated cell surface Ca_v1.2 channels. Signals corresponding to Ca_v1.2 were normalized to that for Na⁺/K⁺ ATPase (surface) or GAPDH (input). Results are from four independent experiments. Statistical significance was determined by Student's t test.