http://emboj.embopress.org/content/embojnl/27/4/692.full.pdf (Any fulltext)
Harzheim, D., Pfeiffer, K. H., Fabritz, L., Kremmer, E., Buch, T., Waisman, A., et al. (2008). Cardiac pacemaker function of HCN4 channels in mice is confined to embryonic development and requires cyclic AMP. EMBO Journal, 27(4), 692-703.