Figure 2. The efficacy of mono-, di- and trivalent ions on SNAP25 clustering in the cell membrane depends on ion charge-to-radius ratio.

(a) Membrane sheets incubated at 37 °C for 10 min with 1 mM chloride salts of Na⁺, Mg²⁺, Ca²⁺, Zn²⁺, Sr²⁺, Y³⁺, Ba²⁺ and La³⁺ (sorted by atomic number), fixed, and immunostained for SNAP25. Overviews are shown at the same, magnified views at arbitrary intensity scaling. (b) The degree of SNAP25 clustering is expressed as rel. SD of the immunostaining pattern, normalized to the control condition. Ions are shown in decreasing order of their clustering efficacy. (c) Plotting values from (b) versus the ratio of ion charge-to-crystal radius²³ shows a distribution resembling a volcano plot (grey lines). For relation to other ion properties see Supplementary Fig. 5. Values are means ± s.e.m.