Figure 2. The effects of rapid removal of K⁺ on caffeine-induced cell shortening in the same cell.

In 0K, cell relaxation in the presence of caffeine, and mostly dependent on Na⁺-Ca²⁺ exchanger activity, was slowed compared with cell relaxation when 6K is present in the superfusing solution. This suggests that inhibition of the Na⁺-K⁺ pump leads to a reduced ability of the Na⁺-Ca²⁺ exchanger to remove Ca²⁺. The bar graph shows data for the monoexponential time constant fitted on the relaxation phase of the traces recorded in 6 cells. ** P < 0.05.