Figure 7.
Essential role for the IQ in CaBP1 binding and modulation of Cav1.2 during repetitive stimuli. A, Effect of alanine substitutions in the IQ on binding of CaBP1 and modulation of Cav1.2. Top panels show CaBP1 binding to GST-tagged fragments containing the IQ with or without IQ-AA substitutions (CT6, CT6IQ-AA). Binding was done with 2 mm Ca2+ as described in Figure 2B. Bottom panel shows pattern of ICa evoked by repetitive stimuli in cells transfected with Cav1.2IQ-AA alone (open circles) or cotransfected with CaBP1 (filled circles). Data were obtained with voltage protocols and plotted as in Figure 6. Points represent mean ± SEM (n = 4-6), with every second point plotted. B, Fractional current obtained in A was averaged for the first 10 (0-0.1 sec) and last 10 (0.9-1 sec) pulses in the train and shown for Cav1.2IQ-AA transfected alone (open bars) or cotransfected with CaBP1 (filled bars) (*p < 0.005 compared with Cav1.2IQ-AA). C, IQ to EE substitutions prevent binding and inhibit functional effects of CaBP1. Top panel shows loss of CaBP1 binding to GST-tagged CT6 with IQ-EE substitutions. Bottom panel shows ICa, obtained as in A, in cells transfected with Cav1.2 channels containing the IQ-EE mutation alone (n = 5; open circles) or cotransfected with CaBP1 (n = 6; filled circles). D, Fractional current for data plotted in C was averaged as in B for Cav 1.2IQ-EE alone (open bars) or Cav1.2IQ-EE plus CaBP1 (filled bars) (* p < 0.05 compared with Cav1.2IQ-EE).