Figure 2. High membrane potential has no effect on the Ca²⁺ pump but inhibits the Na⁺ pump.

A shows the effect on both surface pH and V_Ca of 4 increasing depolarizations followed by 6 injections of CaCl₂. The effect of a 40 mV hyperpolarization on the recovery after the 5th injection is also shown. The preparation was bathed in 1 mm Hepes throughout. B shows the effect of a similar hyperpolarization and later the removal of external K⁺ on the recovery of intracellular Na⁺ after iontophoretic injections (by 40 nA for 30 s). Intracellular Na⁺ was recorded with a NaSM.