Figure 3: Action potential and calcium transient recordings from rabbit (left) and human (right) SA nodal myocytes and associated numerical reconstructions of membrane currents. (a) Recorded membrane potential . (b) Recorded intracellular calcium concentration (). (c) Time derivative of (d). (d) Reconstructed hyperpolarization-activated inward current (). The noisy trace in gray is the net membrane current () computed from , where denotes membrane capacitance. (e) Reconstructed sodium-calcium exchange current (), with the net membrane current in gray.