Cardiac pacemaker cells create rhythmic pulses that control heart rate; pacemaker dysfunction is a prevalent disorder in the elderly, but little is known about the underlying molecular causes. Popeye domain containing (Popdc) genes encode membrane proteins with high expression levels in cardiac myocytes and specifically in the cardiac pacemaking and conduction system. Here, we report the phenotypic analysis of mice deficient in Popdc1 or Popdc2. ECG analysis revealed severe sinus node dysfunction when freely roaming mutant animals were subjected to physical or mental stress. In both mutants, bradyarrhythmia developed in an age-dependent manner. Furthermore, we found that the conserved Popeye domain functioned as a high-affinity cAMP-binding site. Popdc proteins interacted with the potassium channel TREK-1, which led to increased cell surface expression and enhanced current density, both of which were negatively modulated by cAMP. These data indicate that Popdc proteins have an important regulatory function in heart rate dynamics that is mediated, at least in part, through cAMP binding. Mice with mutant Popdc1 and Popdc2 alleles are therefore useful models for the dissection of the mechanisms causing pacemaker dysfunction and could aid in the development of strategies for therapeutic intervention.

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A supramolecular system that switches reversibly, via three different states, through electrochemical adjustment of the guest properties of tetrathiafulvalene (TTF) has been developed. 1H NMR, luminescence, and absorption spectroscopies, in conjunction with LSI mass spectrometry, X-ray crystallography, and cyclic/differential pulse voltammetries, established that the π-electron-accepting (EA) tetrathiafulvalenium dication (TTF2+) binds strongly within the cavity of the π-electron-donating (ED) macrocyclic polyether 1,5-dinaphtho[38]crown-10 (1/5DN38C10), generating a host−guest complex that is stabilized by, inter alia, π−π stacking interactions. Comparable techniques have also demonstrated that neutral tetrathiafulvalene (TTF(0)) acts as an ED guest when it complexes with the EA tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+). On the other hand, the tetrathiafulvalenium radical cation (TTF+•) is not bound by either of the hosts CBPQT4+ or 1/5DN38C10. Electrochemical experiments revealed that the three-component mixture CBPQT4+−1/5DN38C10−TTF behaves as a reversible three-pole supramolecular switch, since, depending on the potential range, TTF can be (1) free (in the TTF+• state), (2) included within the cavity of CBPQT4+ (as TTF(0)), or (3) complexed with 1/5DN38C10 (in the TTF2+ state). The system's three-pole behavior has interesting implications in relation to the design of electrochromic displays and devices capable of controlling energy- or electron-transfer processes between selected components.