Local Na/K pump inhibition results in [Na]i gradients. (A) Na/K pumps were blocked in the area downstream of the glass pipette, placed either in position 1 or 2, with K-free solution flowing through the tip of the pipette. The area upstream of the pipette was exposed to the bath solution, which flows parallel to the longitudinal axis of the myocyte. Initially, the bath solution contained 0 Na, 4 mM K. An the end of the experiment, this was changed to the K-free solution. (B) [Na]i in the three regions indicated in A. The solid bars indicate the application of K-free, 140 mM Na solution via the pipette (Local 1, Local 2) placed in position 1 or 2 (indicated in A) or in the bath solution (Global). (C) ΔF/F0 images of the cell at the moments marked by arrowheads in B. (D) [Na]i distribution along the longitudinal axis of the cell during the two episodes of local Na/K pump blockade at the times indicated by the dashed lines in B.