Figure 3.

Effects of intracellular Na⁺ on the Mg²⁺ association rate constant. (A, left) Single-channel currents recorded with different intracellular Na⁺ concentrations. The extracellular solution contained 150 mM Na⁺ and 7 μM Mg²⁺, and the membrane potential was −80 mV. (A, right) Open interval duration histograms. Because intracellular Na⁺ slows the association of extracellular Mg²⁺, the inverse of open channel lifetime (τ_o) is faster in 5 mM [Na⁺]_in (top histogram) than in 100 mM [Na⁺]_in (bottom histogram). (B) The voltage dependence of the effect of intracellular Na⁺ on the Mg²⁺ association rate constant. The apparent Mg²⁺ association rate is plotted against the membrane potential for different [Na⁺]_in. The solid lines are fits by . The inhibition of Mg²⁺ association by [Na⁺]_in is enhanced by depolarization.