Figure 6. The effect of ATP on Ca²⁺ efflux in the absence of ${\text{Na}}_{\text{i}}^{+}$.

Unless otherwise stated, all concentrations are given as millimolar. The arrows indicate the removal or addition of compounds to the dialysis medium. •, Ca²⁺ efflux in the presence of ${\text{Na}}_{\text{o}}^{+}$. ^, Ca²⁺ efflux in the absence of ${\text{Na}}_{\text{o}}^{+}$. The concentration of vanadate (Van) was 100 μm. Axon diameter, 600 μm. Temperature, 16.5 °C. Note the absence of ATP stimulation of ${\text{Na}}_{\text{o}}^{+}$-dependent Ca²⁺ efflux in the absence of ${\text{Na}}_{\text{i}}^{+}$.