Optical techniques provide information on various effective diffusion coefficients in the presence of traps

SIGAUT, LORENA; PONCE, MARIA LAURA; COLMAN-LERNER, ALEJANDRO; PONCE DAWSON, SILVINA

PHYSICAL REVIEW E - STATISTICAL PHYSICS, PLASMAS, FLUIDS AND RELATED INTERDISCIPLINARY TOPICS

American Physical Society

Año: 2010 vol. 82 p. 519121 - 5191211

1063-651X

In many cell-signaling pathways information is transmitted via the diffusion of messenger molecules. Inmost cases, messengers react with other substances and diffuse at the same time. Effective diffusion coefficientsmay be introduced to characterize the net transport rate that results from the combined effect of thesetwo processes. It was shown in B. Pando et al., Proc. Natl. Acad. Sci. U.S.A. 103, 5338 (2006) that even inthe simplest scenario in which one bimolecular reaction is involved, two different effective coefficients arerelevant. One gives the rate at which small perturbations spread out with time while the other relates the meansquare displacement of a single particle to the time elapsed. They coincide in the absence of reactions but maybe very different in other cases. Optical techniques provide a relatively noninvasive means by which transportrates can be estimated. In the above mentioned paper it was discussed why, under certain conditions, fluorescencerecovery after photobleaching (FRAP), a technique commonly used to estimate diffusion rates in cells,provides information on one of the two effective coefficients. In the present paper we show that, under thesame conditions, another commonly used optical technique, fluorescence correlation spectroscopy (FCS), givesinformation on the other one. This opens up the possibility of combining experiments to obtain information thatgoes beyond effective transport rates. In the present paper we discuss different ways to do so.