Fig. 5. Connexon surface as a function of Ca²⁺ concentration. Extracellular surfaces of connexons displayed in an idealized 2D lattice were recorded in the absence (A) and presence (B) of Ca²⁺. Correlation averages shown were calculated from several topographs recorded under equivalent conditions. The lateral resolution of the averages was limited to ∼1.5 nm. To visualize their differences, a difference map was calculated (C). (D) Superimposed contours of the two conformations (red, no Ca²⁺; green, with Ca²⁺). All presentations show that the most significant change is observed at the pore. The contour plots, however, show that in the presence of Ca²⁺ the connexin surface protrusions move towards the pore center. Note that the greatest difference is in the size of the pore. The images exhibiting a vertical gray level range of 2 nm (A and B) and 0.8 nm (C) were displayed as relief tilted by 5°.