Hypertonicity increases cAMP in PMN and blocks oxidative burst by PKA-dependent and -independent mechanisms.
Hypertonic stress (HS) suppresses neutrophil (PMN) functions. We studied the underlying mechanism and found that HS rapidly (<1 min) increased intracellular cAMP levels by up to sevenfold. cAMP levels correlated with applied hypertonicity and the degree of neutrophil suppression. HS and cAMP-elevating drugs (forskolin and dibutyryl cAMP-acetoxymethyl ester) similarly suppressed extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase activation and superoxide formation in response to N-formylmethionyl-leucyl-phenylalanine (fMLP) stimulation. Inhibition of cAMP-dependent protein kinase A (PKA) with H-89 abrogated the suppressive effects of HS, restoring fMLP-induced ERK and p38 activation and superoxide formation. Inhibition of phosphodiesterase with 3-isobutyl-1-methylxanthine augmented cAMP accumulation and the suppressive effects of HS, while inhibition of adenylyl cyclase with MDL-12330A abolished these effects. These findings suggest that HS-activated cAMP/PKA signaling inhibits superoxide formation by intercepting fMLP-induced activation steps upstream of ERK and p38. In contrast to its effects in the presence of moderate hypertonicity levels (40 mM), H-89 was unable to rescue neutrophil functions from suppression by higher hypertonicity levels (100 mM), indicating that more severe HS suppresses neutrophils via secondary PKA-independent mechanisms.
Orlic
Tatjana
T
Surgical Immunology Research Laboratory, Department of Surgery, Division of Trauma, University of California, San Diego, California 92103-8236, USA.
Loomis
William H
WH
Shreve
Amy
A
Namiki
Sachiko
S
Junger
Wolfgang G
WG
D000067956:Adenylyl Cyclase Inhibitors; D003994:Bucladesine / Q000031:analogs & derivatives / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006982:Hypertonic Solutions / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D016897:Respiratory Burst / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013481:Superoxides / Q000378:metabolism
D000067956:Adenylyl Cyclase Inhibitors; D004791:Enzyme Inhibitors; D006982:Hypertonic Solutions; D010726:Phosphodiesterase Inhibitors; D013481:Superoxides; D009240:N-Formylmethionine Leucyl-Phenylalanine; D003994:Bucladesine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases