Figure 11. The effect of alkaline phosphatase injection on the Pa and ATP stimulation of ${\text{Na}}_{\text{o}}^{+}$-dependent Ca²⁺ efflux (${\text{Na}}_{\text{i}}^{+}$-${\text{Ca}}_{\text{o}}^{2+}$ exchange).

A and B: •, Ca²⁺ efflux in the presence of ${\text{Na}}_{\text{o}}^{+}$. ^, Ca²⁺ efflux in the absence of ${\text{Na}}_{\text{o}}^{+}$. The arrows indicate the removal or addition of Pa, ATP or vanadate (Van), or the intracellular injection of alkaline phosphatase. Nine units of alkaline phosphatase were injected into each axon in a total volume of 0.16 μl. Note that both Pa and ATP stimulation of ${\text{Na}}_{\text{o}}^{+}$-dependent Ca²⁺ efflux are inhibited by the exogenous phosphatase. The inhibition is complete for the case of ATP and only partial in the case of Pa. Axon diameter: A, 575 μm; B, 600 μm. Temperature, 17 °C.