Figure for Ca2+ dynamics. Draw a model with arrows and #’s inthe order

“The scheme of ionic currents within a cardiac cycle for amammalian pacemaker cell”

The scheme of ionic currents within a cardiac cycle for amammalian pacemaker cell (i.e., SA node) is generally describedwith the background [Ca2+]i continually increasing and decreasing.Starting in diastolic depolarization with a slow release of Ca2+ byryanodine receptors (RyR), from the SR, leads to a rise in [Ca2+]i. The SERCA pumps Ca2+ back into the SR and the NCX removes [Ca2+]iin exchange for Na+ ions across the plasma membrane of the cell.The influx of Na+ ions can lead to a depolarization of the plasmamembrane. Thus, opening low voltage-gated T-type Ca2+ channels(VCa) (Hüser et al. 2000) and potentially voltagegated Na+channels. The influx of Ca2+ acts on the RyR to cause the ER todump Ca2+ which results in a calcium induced inhibition of the RyR.Until the [Ca2+]i is reduced by the SERCA and NCX, the RyR stayinhibited but will start leaking Ca2+ as [Ca2+]i returns to a lowlevel to then repeat the cycle (Subramani and Subbanna, 2006). Inthe mammalian heart, the pace making sinus node cells do notcontain a K+ current (IK1) which is thought to be one reason thepacing cells do not show a resting membrane potential (Opthof,2007).