Bound attractant at the leading vs. the trailing edge determines chemotactic prowess

doi:10.1073/pnas.0705889104

Bound attractant at the leading vs. the trailing edge determines chemotactic prowess

Departments of *Cellular and Molecular Pharmacology and
^¶Biochemistry and Biophysics, University of California, 600 16th Street, San Francisco, CA 94158; and
^‡Department of Physics, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093

Contributed by Henry R. Bourne, July 2, 2007 (received for review May 11, 2007)

Abstract

We have analyzed chemotaxis of neutrophil-differentiated HL60 cells in microfluidic devices that create exponential gradients of the chemoattractant, f-Met-Leu-Phe (fMLP). Such gradients expose each cell to a difference in fMLP concentration (ΔC) across its diameter that is directly proportional to the ambient concentration (C) at that cell's position in the gradient, so the ratio ΔC/C is constant everywhere. Cells exposed to ambient fMLP concentrations near the constant of dissociation (K _d) for fMLP binding to its receptor (≈10 nM) crawl much less frequently when ΔC/C is 0.05 than when it is 0.09 or 0.13. Hence, cells can detect the gradient across their diameter without moving and, thus, without experiencing temporal changes in attractant concentration. At all ΔC/C ratios tested, the average chemotactic prowess of individual cells (indicated by the distance a cell traveled in the correct direction divided by the length of its migration path) is maximal for cells that start migrating at concentrations near the K _d and progressively decreases at higher or lower starting concentrations.

Footnotes

^‖To whom correspondence may be addressed at:
University of California at San Diego, Urey Hall, MC 0374, 9500 Gilman Drive, La Jolla, CA 92093.
E-mail: agroisman{at}ucsd.edu
**To whom correspondence may be addressed at:
University of California, N212F, Box 2140, 600 16th Street, San Francisco, CA 94158-2140.
E-mail: bourne{at}cmp.ucsf.edu
Author contributions: P.H. and H.R.B. designed research; P.H., F.W., and K.W. performed research; K.C. contributed new reagents/analytic tools; P.H., H.E.-S., A.G., and H.R.B. analyzed data; and P.H., H.E.-S., A.G., and H.R.B. wrote the paper.
↵ ^†Present address: Department of Molecular and Cell Biology, University of California, 479 Life Science Addition, Berkeley, CA 94720-3200.
↵ ^§Present address: University of Illinois, Chemical and Life Sciences Laboratory (CLSL), B107, 601 South Goodwin Avenue, Urbana, IL 61801.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0705889104/DC1.
Abbreviations:

C,

concentration;

ΔC,

difference in fMLP concentration;

CI,

chemotactic index;

fMLP,

f-Met-Leu-Phe.
Freely available online through the PNAS open access option.