Figure 3.

Extracellular Ca²⁺ inhibits I_AP and extracellular K⁺ is required for I_AP. (A) Whole-cell currents recorded in a bath solution with zero mM KCl and 40 mM CaCl₂ show inhibition of I_AP. (B) I_AP was restored when the bath was perfused with a standard bath solution containing 30 mM KCl, 1 mM CaCl₂. I_AP was recorded in the same cell as in A. Similar results were found in eight cells. Arrows show zero current levels in A and B. (C) Average effects of extracellular Ca²⁺ and K⁺ concentrations on I_AP (n = 5–8). A pipette solution with nominally zero Ca²⁺ and bath solutions with varying Ca²⁺ and K⁺ concentrations as indicated (in mM) were used.