Fig. 6. Effect of directly loading NCX_IF into the cytoplasm on I_NCX during the [Ca²⁺]_i decline.

The caffeine-evoked I_NCX and [Ca²⁺]_i were simultaneously recorded and plotted as described in Figs. 4 and 5. The data were obtained by taking the decline phase of the caffeine-induced Ca²⁺ transient (starting from the I_NCX peak until the baseline was reached). A. The average I_NCX values (for given [Ca²⁺]_i levels) were plotted for NCX_IF-loaded or control cardiomyocytes (-NCX_IF). B. The I_NCX/[Ca²⁺]_i curves were fitted by linear regression and the obtained slopes were averaged as indicated (n = 9 for control cells and n = 12 NCX_IF-loaded cells, P < 0.001). The n values represent the number of independent experiments. C. The observed ranges of [Ca²⁺]_i values (obtained in each specific experiment) were plotted vs. I_NCX, as described in Fig. 5.