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GTP-related difference in cyclic AMP production between resident and inflammatory human peritoneal macrophages
A P Houdijk1, P A Van Leeuwen, M J Adolfs
1Department of Surgery, Free University Hospital, Amsterdam, The Netherlands.
Abstract:
In macrophages cyclic AMP (c-AMP) plays an important role in regulating many activities such as phagocytosis, migration and tumoricidal activity. High intracellular levels of c-AMP are negatively correlated with these activities. In earlier studies we have shown that c-AMP levels in inflammatory human peritoneal macrophages (IM) were markedly lower when compared to levels in resident macrophages (RM). This is in line with the fact that c-AMP down-regulates macrophage activity. To our knowledge no data are available on the mechanism underlying the difference in c-AMP production between RM and IM. In this study the difference in c-AMP production between RM and IM has been investigated on the level of receptor and G-protein-related mechanisms. Macrophage membranes were incubated with different agents i.e. prostaglandin E2 (PGE2), prostacyclin I2 (PGI2), isoprenalin (ISO) and sodium fluoride (SF). Additionally, the capacity of IM and RM to hydrolyse quanosine triphosphate (GTP) was measured. Only in the presence of GTP (10(-4) M) could the c-AMP difference be detected (RM = 51 +/- 4.4 pmol/mg protein/min +/- S.E., n = 22, IM = 32.8 +/- 5.2 pmol/mg protein/min +/- S.E., n = 10, p less than 0.01). After receptor stimulation with PGE2, PGI2 and ISO, c-AMP levels increased to the same extent in both IM and RM with no effect on the GTP-related difference. After SF stimulation, c-AMP levels in RM and IM increased to the same level (RM = 63 +/- 8 pmol/mg protein/min, n = 14, IM = 58 +/- 11 pmol/mg protein/min, n = 13).(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Inflammatory macrophages have lower cyclic AMP (c-AMP) levels than resident macrophages, but receptor stimulation does not explain this difference. G-protein activity appears to be involved in regulating c-AMP production in macrophages.
Area of Science:
- Immunology
- Cellular Biology
- Biochemistry
Background:
- Cyclic AMP (c-AMP) is a crucial second messenger regulating macrophage functions like phagocytosis and migration.
- High intracellular c-AMP levels are inversely correlated with macrophage activity.
- Previous studies indicated lower c-AMP levels in inflammatory macrophages (IM) compared to resident macrophages (RM).
Purpose of the Study:
- To investigate the underlying mechanisms responsible for the difference in c-AMP production between RM and IM.
- To explore the roles of receptor and G-protein-related mechanisms in regulating c-AMP levels.
Main Methods:
- Macrophage membranes from RM and IM were incubated with various agents: prostaglandin E2 (PGE2), prostacyclin I2 (PGI2), isoprenalin (ISO), and sodium fluoride (SF).
- The capacity of RM and IM to hydrolyze guanosine triphosphate (GTP) was measured.
- c-AMP levels were quantified after stimulation with different agents and in the presence of GTP.
Main Results:
- A significant difference in c-AMP production between RM and IM was only detected in the presence of GTP (RM: 51 ± 4.4 pmol/mg protein/min; IM: 32.8 ± 5.2 pmol/mg protein/min).
- Receptor stimulation with PGE2, PGI2, and ISO increased c-AMP levels similarly in both RM and IM, without altering the GTP-related difference.
- Sodium fluoride stimulation led to comparable increases in c-AMP levels in both RM and IM.
Conclusions:
- The difference in c-AMP production between RM and IM is not solely explained by receptor-mediated signaling.
- G-protein mediated signaling, particularly in the presence of GTP, plays a significant role in the observed differences in c-AMP levels between macrophage populations.
- Further investigation into G-protein function is warranted to fully understand c-AMP regulation in inflammatory versus resident macrophages.