LOCOMOTIVE FORCES PRODUCED BY SINGLE LEUKOCYTES IN-VIVO AND IN-VITRO

We report here the first time-resolved measurements of the forces prod uced during the migration of single leukocytes in vivo and in vitro. P ulmonary macrophages from hamsters and mice, in vitro, and Nembutal (p entobarbital sodium)-anesthetized hamster neutrophils, in vivo, genera ted maximum locomotive forces ranging from 1.9 to 10.7 nN or tenths of microdynes. Force production was periodic and correlated with the len gth of the leading lamellipod but not with generalized cell ruffling. Although the extension of the leading lamella is critical to locomotiv e force generation, these direct measurements suggest that lamellar ex tension may not arise from the same contractile processes driving forw ard motion of the cell mass. Indeed, cell ruffling, lamellar extension , and locomotive force generation may be differentially controlled and have different origins. This technique may be extended to test numero us hypotheses of how these and other nonmuscle cells crawl.