Conversion of Ca oscillation into propagative electrical signals by Ca-activated ion channels and connexin as a reconstituted Ca clock model for the pacemaker activity.

Conversion of intracellular Ca signals to electrical activity results in multiple and differing physiological impacts depending on cell types. In some organs such as gastrointestinal and urinary systems, spontaneous Ca oscillation in pacermaker cells can function essentially as a Ca clock mechanism, which has been originally found in pacemaking in sinoatrial node cell of the heart. The conversion of discrete Ca clock events to spontaneous electrical activity is an essential step for the initiation and propagation of pacemaker activity through the multicellular organs resulting in synchronized physiological functions. Here, a model of intracellular signal transduction from a Ca oscillation to initiation of electrical slow waves and their propagation were reconstituted in HEK293 cells. This was accomplished based on ryanodine receptor (RyR) type 3, Ca-activated ion channels, i.e. small conductance Ca-activated K channel (SK2) or Ca-activated Cl channel (TMEM16A), and connexin43 being heterologously co-expressed. The propagation of electrical waves was abolished or substantially reduced by treatment with selective blockers of the expressed channels and 18β-glycyrrhetinic acid, a gap junction inhibitor, respectively. Thus, we demonstrated that the conversion of Ca oscillation to electrical signals with cell to cell propagation can be reconstituted as a model of Ca clock pacemaker activity by combinational expression of critical elements in heterologous expression system.