Receptor-recognized alpha 2-macroglobulin-methylamine elevates intracellular calcium, inositol phosphates and cyclic AMP in murine peritoneal macrophages.
Human plasma alpha 2-macroglobulin (alpha 2M) is a tetrameric proteinase inhibitor, which undergoes a conformational change upon reaction with either a proteinase or methylamine. As a result, a receptor recognition site is exposed on each subunit of the molecule enabling it to bind to its receptors on macrophages. We have used Fura-2-loaded murine peritoneal macrophages and digital video fluorescence microscopy to examine the effects of receptor binding on second messenger levels. alpha 2M-methylamine caused a rapid 2-4-fold increase in intracellular Ca2+ concentration ([Ca2+]i) within 5 s of binding to receptors. The agonists induced a focal increase in [Ca2+]i that spread out to other areas of the cell. The increase in [Ca2+]i was dependent on the alpha 2M-methylamine concentration and on the extracellular [Ca2+]. Both sinusoidal and transitory oscillations were observed, which varied from cell to cell. Neither alpha 2M nor boiled alpha 2M-methylamine, forms that are not recognized by the receptor, affected [Ca2+]i in peritoneal macrophages under identical conditions of incubation. The alpha 2M-methylamine-induced rise in [Ca2+]i was accompanied by a rapid and transient increase in macrophage inositol phosphates, including inositol tris- and tetrakis-phosphates. Native alpha 2M did not stimulate a rise in inositol phosphates. Finally, binding of alpha 2M-methylamine to macrophages increased cyclic AMP transiently. Thus receptor-recognized alpha-macroglobulins behave as agonists whose receptor binding causes stimulation of signal transduction pathways.
Misra
U K
UK
Department of Pathology, Duke University Medical Center, Durham, NC 27710.
Chu
C T
CT
Rubenstein
D S
DS
Gawdi
G
G
Pizzo
S V
SV
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008744:Methylamines / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D010529:Peritoneal Cavity / Q000166:cytology; D000511:alpha-Macroglobulins / Q000378:metabolism / Q000494:pharmacology*
D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D008744:Methylamines; D000511:alpha-Macroglobulins; C027451:methylamine; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2