F-actin network formation in tethers and in pseudopods stimulated by chemoattractant.
Micropipets are used either to deliver a given concentration of the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP) to a local region of a human neutrophil or to create a membrane tether. Pseudopods, which have a cylindrical shape and grow at a constant rate, are formed in either case. After reaching a maximum extension, they retract, even in the presence of chemoattractant. As a pseudopod grows, cell granules begin to penetrate the pseudopod region to a "boundary" that defines a distance to the pseudopod's leading edge that is almost constant. The exclusion of granules from this domain indicates that it is filled with a dense network. The formation of this network involves the plasma membrane because pseudopod growth ceases when a membrane tether is pulled away from the leading edge. The rate of pseudopod growth depends on fMLP concentration just as the number of occupied N-formyl peptide receptors depends on this concentration. The experimental data are explained by assuming that F-actin network is formed next to the plasma membrane. The newly formed network displaces the membrane and the dominant process in the network region then becomes F-actin depolymerization. The rate of pseudopod growth is determined by the rate of the process leading to network formation. This process is apparently an enzymatic type of reaction. It has a positive enthalpy change and, therefore, is endothermic.
Zhelev
D V
DV
Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708-0300, USA.
Alteraifi
A M
AM
Hochmuth
R M
RM
D000199:Actins / Q000378:metabolism*; D002465:Cell Movement / Q000502:physiology; D002630:Chemotactic Factors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008954:Models, Biological; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects; D011554:Pseudopodia / Q000187:drug effects / Q000502:physiology*
D000199:Actins; D002630:Chemotactic Factors; D009240:N-Formylmethionine Leucyl-Phenylalanine