Fig. 5.

Dependence of Na⁺/Ca²⁺ exchange on intracellular [K⁺]. Activity of Na⁺/Ca²⁺ exchange was estimated from the difference (γ_Na−Li) between the Ca²⁺ decay rate at 145 mm[Na⁺]_o (γ_Na) and the decay rate (γ_Li) at 20 mm[Na⁺]_o (Na⁺ was replaced with iso-osmolar Li⁺). Mean values of γ_Na−Li obtained from n axon terminals were plotted as a function of [K⁺]_i(error bars indicate SEM). The internal K⁺dependence of γ_Na−Li was fitted using the following Michaelis–Menten equation (solid line): 0.07/sec + (0.90/sec · [K⁺]_i)/([K⁺]_i+ 30.3 mm).