Figure 3. Permeation of monovalent and divalent cations through channels activated by dialysis of IP₃ in CHO(CCE1) and CHO(-) cells.

Ionic currents were recorded in CHO(CCE1) cells in the presence of extracellular Ba²⁺ (A) and with either external Na⁺ or Ca²⁺ in the presence of Mg²⁺ (B). Currents recorded with external Na⁺ in CHO(CCE1) (C) and CHO(-) (D) were blocked by extracellular Ca²⁺ in the absence of Mg²⁺. External concentrations of Ba²⁺ (${\text{Ba}}_{\text{o}}^{\text{2+}}$), Na⁺ (${\text{Na}}_{\text{o}}^{\text{2+}}$) and Mg²⁺ (${\text{Mg}}_{\text{o}}^{\text{2+}}$) are millimolar. The external concentration of Ca²⁺ is given as pCa_o. The intracellular concentration of Cs⁺ was 115 mM.