Figure 12. Effect of high [Na⁺]_i on the stimulation by PA of the forward Na⁺–Ca²⁺ exchange in axons dialysed with low and high [Ca²⁺]_i.

Filled symbols correspond to the efflux of Ca²⁺ in the presence of 3 mm ${\text{Ca}}_{\text{o}}^{2+}$ and no ${\text{Na}}_{\text{o}}^{+}$ (forward exchange). Open symbols represent the efflux of Ca²⁺ in the absence of both extracellular Na⁺ and Ca²⁺ (unspecific and/or leak fluxes). The inclusion and/or withdrawal of intra- and extracellular ligands are indicated on top of the figure. The ligands and units of concentration are given on the left and the actual concentrations over the corresponding line. The pH_i, [Na⁺]_i and [Ca²⁺]_i are given in the insert. Note: (i) Li⁺ was used as an inert Na⁺ replacement; and (ii) the fractional PA stimulation of Ca²⁺ efflux is similar at 5 μm and 500 μm ${\text{Ca}}_{\text{i}}^{2+}$. Ordinate: Ca²⁺ efflux (fmol cm⁻² s⁻¹). Abscissa: time (min). See text for details.