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Fig. 2 Interaction of POPDC proteins with the cardiac sodium channel Nav1.5 or the skeletal muscle sodium channel Nav1.4 (A) Co-immunoprecipitation of POPDC2-FLAG with Nav1.5-HA was performed in COS-7 cells using anti-HA antibodies. An empty vector served as control. The co-immunoprecipitation was subsequently detected with an anti-FLAG antibody (IB: α-Flag). (B) Co-immunoprecipitation of POPDC2 and Nav1.5 in murine heart lysates (mheart) using anti Nav1.5 antibodies (IP: α-Nav1.5). The immunoprecipitation was subsequently detected with an anti-Nav1.5 (IB: α-Nav1.5) and the co-immunoprecipitation by an anti-POPDC2 antibody (IB: α-POPDC2). HeLa cells were used as a control. (C) Oocytes were injected with cRNA for human Nav1.5 or co-injected with different murine POPDC isoforms and subsequently stored in a storage solution lacking theophylline. Currents were recorded with a P/N (N = 4) voltage-step protocol (holding potential −80 mV) and voltage-steps of 50 ms ranging from −70 to +80 mV in 10 mV increments (see inset). (D and E) (D) Relative current amplitudes analyzed at −20 mV and normalized to Nav1.5. (E) Voltage-dependence of Nav1.5 activation in the absence or presence of POPDC1, POPDC2 or POPDC3. The respective voltages of half-maximal activation (V1/2) and the Boltzmann constants (k) are provided as inset. The number of technical replicates (n) is indicated in parentheses or bar graphs. Data are presented as mean ± s.e.m. Significance was probed using a two-sided Student’s t-test. ∗∗∗, p < 0.001. (F and G) (F) POPDC2 does not modulate current amplitudes of Nav1.4, analyzed at −10 mV and normalized to Nav1.4 or (G) the shape of the voltage-dependence of Nav1.4 activation. The respective voltages of half-maximal activation (V1/2) and the Boltzmann constants (k) are provided as inset. The number of technical replicates (n) is indicated in parentheses or bar graphs. Oocytes were stored in a storage solution lacking theophylline. Data are presented as mean ± s.e.m. Significance was probed using a two-sided Student’s t-test. See also Figures S1 and S2.