Concentration profiles obtained from the simulation for 1000

<p> <b>cells/cm²</b> (<b>a</b>) <b>and 10,000 cells/cm²</b> (<b>b</b>) <b>at t = 48 </b><b>hours.</b> Concentrations are in units of pM. For this data, <i>r</i> = 5×10⁻¹³ moles/m²/s (approximately 10 molecules/cell/s), <i>k_on</i> = 10⁸ 1/(M.min), <i>R</i> = 10⁵ receptors per cell, diffusion co-efficient = 10⁻¹⁰ m²/s. More detailed models are described in the supporting information (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051796#pone.0051796.s004" target="_blank">Text S2</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051796#pone.0051796.s005" target="_blank">Text S3</a>).