Figure 2.

The signaling efficacy of a single NO-producing fiber critically depends on its diameter. A, The NO concentration at the fiber surface declines dramatically for thinner fibers. Surface concentrations after 1 s of continuous synthesis are 440, 25.5, and 0.37 nm for fiber diameters of 5, 1, and 0.1 μm, respectively (diameters chosen with reference to B). The inset in A shows the graph at a larger scale for diameters below 0.5 μm. B, The problem of the lower surface concentration of thinner fibers is exacerbated by a steeper decline of the NO concentration as one moves away from the fiber surface. NO concentration is plotted over distance from the fiber surface as percentage of the surface concentration for fiber diameters of 5 μm (solid line in B), 1 μm (dashed line in B), and 0.1 μm (dotted line in B). Note, however, that even very thin (0.1 μm) fibers reach ∼20% of the surface concentration 20 μm away from the surface after 1 s of synthesis (hairlines in B). This extensive spread is the basis of cooperative volume signaling (compare with Fig. 4).