KChIP2 knock down enhances density of L-type Ca2+ current.

<p><b>(A)</b> Representative <i>I</i>_{<i>Ca</i>,<i>L</i>} current traces of control and KChIP2 KD treated cells following 24 hrs incubation. Currents were elicited from a holding potential of -40 mV and a depolarizing step to 10 mV. <b>(B)</b> I/V curve summary data of <i>I</i>_{<i>Ca</i>,<i>L</i>} displays significant enhancement of current density following KChIP2 KD (n = 12) compared to control cardiomyocytes (n = 20), explaining the prolonged plateau phase of the cardiac action potential. <b>(C)</b> Steady-state activation of <i>I</i>_{<i>Ca</i>,<i>L</i>} in control and KChIP2 KD treated myocytes. The data, depicted as normalized conductance, was fit with a Boltzmann curve but no significant difference was detected at any test pulse. <b>(D)</b> Evaluation of current decay kinetics between control and KChIP2 KD treated myocytes at several membrane voltages. <i>τ</i>-values were derived from single exponential fits of <i>I</i>_{<i>Ca</i>,<i>L</i>} decay following channel activation, also showing no significant difference at any test pulses. <b>(E)</b> Left panel shows representative immunoblots for Cav1.2 protein from whole cell lysates for control and KChIP2 KD treated myocytes. Protein expression was normalized to pan-cadherin expression. Right panel shows summary data depicting the normalized, relative densitometry of Cav1.2 expression, resulting in significantly increased expression following KChIP2 KD (n = 4). Data presented as mean ± SEM; <i>*P</i> < 0.05, <i>**P</i> < 0.01; two-tailed Student’s <i>t</i>-test performed for I/V plot, paired two-tailed Student’s <i>t</i>-test performed for Western blot.