Figure 8.

Permeation of external Ca²⁺ and Mg²⁺ in wild-type and E340G mutant channels. Current recordings from individual outside-out patches in bi-ionic conditions. The patch pipette contained 1 mM cGMP and 110 mM NaCl, while the external solution contained either 110 mM NaCl, 73.3 mM CaCl₂, or 73.3 mM MgCl₂, as indicated in the figure. Voltage was changed in 20-mV steps from −80 to +80 mV from a holding potential of 0 mV. The dashed lines indicate the zero-current level. Raw data are illustrated without leak subtraction. Capacitance artifacts were not subtracted. Current–voltage relations are plotted in C and D for wild-type and E340G, respectively. Symbols indicate the bi-ionic conditions: symmetrical NaCl (○), internal NaCl and external CaCl₂ (▴), and internal NaCl and external MgCl₂ (□).