Quantifying noise levels of intercellular signals.

Cells often measure their local environment via the interaction of diffusible chemical signals with cell surface receptors. At the level of a single receptor, this process is inherently stochastic, but cells can contain many such receptors which can reduce the variability in the detected signal by suitable averaging. Here, we use explicit Monte Carlo simulations and analytical calculations to characterize the noise level as a function of the number of receptors. We show that the residual level approaches zero and that the correlation time, i.e., the waiting time needed to obtain statistically independent data, diverges, both for large receptor numbers. This result has important implications for such processes as eukaryotic chemotaxis.