Binding of ¹²⁵I-apamin to K_Ca2.3.

<p>A Time course of ¹²⁵I-apamin binding to HEK 293 cells stably expressing K_Ca2.3. The <i>y</i> axis shows specific binding of ¹²⁵I-apamin at times indicated on the <i>x</i>-axis. Each point represents the mean of triplicate observations from a single experiment. The data are fitted by a single exponential function (solid line) with a rate constant of 0.2±0.05 min^–1_, suggesting binding reaches equilibrium within 10 minutes. B Equilibrium binding of ¹²⁵I-apamin to HEK 293 cells stably expressing K_Ca2.3. The graph shows total (▪) and non-specific (•) binding in the presence of label. Each point is the mean of triplicate observations from a single experiment. Combined data yielded estimates of <i>K</i>_L and <i>B</i>_max of 711±226 pM and 175±18 fmol/10⁶ cells. Solid lines represent a linear fit (non-specific binding) or a fit using the modified Hill equation for <i>B</i>_tot (see methods). C Inhibition of ¹²⁵I-apamin binding to K_Ca2.3 by unlabelled apamin. Each point is the mean of triplicate observations from a single experiment. Data were fitted to the Hill equation (solid line). Estimates of <i>K</i>_L from saturation binding experiments were used to estimate <i>K</i>_i as described in the methods section and the derived values are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073328#pone-0073328-t001" target="_blank">Table 1</a>.