ABSTRACT: Cav1.3 L-type Ca(2+) channel is known to be highly expressed in neurons and neuroendocrine cells. However, we have previously demonstrated that the Cav1.3 channel is also expressed in atria and pacemaking cells in the heart. The significance of the tissue-specific expression of the channel is underpinned by our previous demonstration of atrial fibrillation in a Cav1.3 null mutant mouse model. Indeed, a recent study has confirmed the critical roles of Cav1.3 in the human heart (Baig, S. M., Koschak, A., Lieb, A., Gebhart, M., Dafinger, C., Nürnberg, G., Ali, A., Ahmad, I., Sinnegger-Brauns, M. J., Brandt, N., Engel, J., Mangoni, M. E., Farooq, M., Khan, H. U., Nürnberg, P., Striessnig, J., and Bolz, H. J. (2011) Nat. Neurosci. 14, 77-84). These studies suggest that detailed knowledge of Cav1.3 may have broad therapeutic ramifications in the treatment of cardiac arrhythmias. Here, we tested the hypothesis that there is a functional cross-talk between the Cav1.3 channel and a small conductance Ca(2+)-activated K(+) channel (SK2), which we have documented to be highly expressed in human and mouse atrial myocytes. Specifically, we tested the hypothesis that the C terminus of Cav1.3 may translocate to the nucleus where it functions as a transcriptional factor. Here, we reported for the first time that the C terminus of Cav1.3 translocates to the nucleus where it functions as a transcriptional regulator to modulate the function of Ca(2+)-activated K(+) channels in atrial myocytes. Nuclear translocation of the C-terminal domain of Cav1.3 is directly regulated by intracellular Ca(2+). Utilizing a Cav1.3 null mutant mouse model, we demonstrate that ablation of Cav1.3 results in a decrease in the protein expression of myosin light chain 2, which interacts and increases the membrane localization of SK2 channels.
