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Membrane activity and topography of F-Met-Leu-Phe-Treated polymorphonuclear leukocytes. Acute and sustained responses
B H Davis1, R J Walter, C B Pearson
1Department of Pathology, University of Connecticut Health Center, Farmington.
Abstract:
The chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (f-Met-Leu-Phe) causes a dramatic stimulation of membrane ruffling and a fluid pinocytosis in polymorphonuclear leukocytes (PMNs). These responses are maximal by 1 minute and subside within 5-10 minutes. The same immediate responses characterize cells exposed to several peptide hormones and may thus represent an essential component of target cell activation by peptides. The stimulation of the whole membrane following f-Met-Leu-Phe binding is succeeded by the development of a polarized cell shape with a posterior uropod and a broad anterior lamellipodium, both subtended by microfilaments. Membrane components and functions segregate into distinct domains on polarized PMNs. Thus, succinyl concanavalin A-receptor complexes are capped and internalized by receptor-mediated endocytosis at the uropod; the uptake by fluid pinocytosis of fluorescein-dextran is restricted to the uropod; and coated pits and coated vesicles are concentrated at the uropod. The lamellipodium excludes coated pits and lacks pinocytic activity but shows preferential binding of immunoglobulin aggregates, presumably to Fc receptors. The origin and physiologic implications of these asymmetries of membrane molecular and functional topography on polarized cells are discussed.
Insights
The peptide N-formylmethionyl-leucyl-phenylalanine (f-Met-Leu-Phe) rapidly activates polymorphonuclear leukocytes (PMNs), causing membrane changes and cell polarization. This polarization leads to distinct membrane domains for functions like endocytosis and pinocytosis.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Chemotactic peptides like f-Met-Leu-Phe are crucial for immune cell activation.
- Polymorphonuclear leukocytes (PMNs) are key players in the innate immune response.
- Peptide hormones trigger rapid cellular responses.
Purpose of the Study:
- To investigate the immediate effects of f-Met-Leu-Phe on PMN membrane dynamics.
- To understand the development of cell polarization and membrane domain segregation in PMNs.
- To explore the functional implications of polarized membrane topography.
Main Methods:
- Stimulation of PMNs with f-Met-Leu-Phe.
- Observation of membrane ruffling and fluid pinocytosis.
- Analysis of cell shape changes and development of uropod and lamellipodium.
- Tracking of membrane component segregation (e.g., receptor complexes, fluorescein-dextran, coated pits, immunoglobulin aggregates).
Main Results:
- f-Met-Leu-Phe induced rapid membrane ruffling and fluid pinocytosis in PMNs.
- Cells polarized into a uropod and lamellipodium structure.
- Distinct membrane domains formed: uropod specialized for endocytosis and pinocytosis, lamellipodium for Fc receptor binding.
- Coated pits and vesicles were concentrated in the uropod.
Conclusions:
- f-Met-Leu-Phe triggers rapid, transient PMN activation involving membrane dynamics.
- Cell polarization leads to functional and molecular asymmetry in the PMN membrane.
- These polarized membrane domains are critical for directed cell migration and immune functions.