Figure 7.

AP-clamp currents with 10 mmol/L [Na⁺]_i and K⁺ currents blocked. Top panel shows AP waveform used to voltage-clamp a cardiomyocyte with Cs⁺ substitution of K⁺ in all solutions (to eliminate contamination by Ca²⁺ -activated Cl⁻ current; this experiment was carried out in a guinea pig cardiomyocyte). Under these conditions, the predominant membrane currents were I_Ca,L and I_NCX. The kinetics and direction of the membrane currents during the AP plateau corresponded to estimates of the NCX driving force (magenta trace) calculated from the simultaneously recorded [Ca²⁺]_i transient (red trace).