Neutrophils are hyperpolarized after exudation and show an increased depolarization response to formyl-peptide but not to phorbol myristate acetate

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Abstract
The migration of polymorphonuclear leucocytes (PMN) to extravascular sites and the interaction with chemotactic substances at such locations is called exudation. Since stimulation of PMN in vitro modifies the characteristics of PMN, we asked the question whether similar modifications take place during in-vivo exudation. We found that resting guinea-pig peritoneal exudate PMN were hyperpolarized in comparison to blood PMN of the same species. Guinea-pig and human exudate PMN responded to lower N-formylmethionylleucylphenylalanine (fmet-leu-phe) concentrations than blood PMN and exhibited a larger membrane depolarization. Furthermore, experiments with the fluorescence-activated cell sorter revealed increased forward light scatter from resting exudate PMN compared to blood PMN. Experiments with the fluorescence-activated cell sorter using the fluoresceinated ligand fmet-leu-phe-lysin-fluorescein (fmet-leu-phe-lys-F) indicated that the priming of exudate PMN was associated with increased fmet-leu-phe-lys-F binding on the individual cells. In contrast, phorbol myristate acetate (PMA) did not induce an increased membrane depolarization response in human and guinea-pig exudate PMN. With this stimulus, the only sign of priming was the shorter activation time in exudate PMN compared to blood PMN. Thus, in-vivo exudation modifies the characteristics of resting and stimulated PMN. The priming is different for different stimuli. Increased responsiveness to fmet-leu-phe may be due to fmet-leu-phe receptor upregulation. The distinct characteristics of exudate PMN that we describe may allow definition of clinical situations in which PMN are primed in vivo.

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