Chemoattractant-elicited alterations of cAMP levels in human polymorphonuclear leukocytes require a Ca2+-dependent mechanism which is independent of transmembrane activation of adenylate cyclase.
The affinity of the chemoattractant receptor for N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) on human polymorphonuclear leukocytes (PMNs) is regulated by guanine nucleotides, and chemoattractants stimulate increased intracellular cAMP levels in PMNs. Our data, however, indicate that this receptor does not activate membrane-bound adenylate cyclase via direct nucleotide regulatory protein (N) coupling but instead raises cAMP levels indirectly via a mechanism which appears to require Ca2+ mobilization. This conclusion is based on the following data: 1) prostaglandin E1 (PGE1) activated and alpha 2-adrenergic treatment inhibited adenylate cyclase activation in PMN plasma membranes; fMet-Leu-Phe, however, neither activated nor inhibited adenylate cyclase in these membranes; 2) depletion of extracellular Ca2+ had no effect on isoproterenol and PGE1 elicited cAMP responses in intact PMNs while peak fMet-Leu-Phe and A23187-induced responses were reduced by approximately 50 and 80%, respectively; 3) 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate, a purported Ca2+ antagonist, caused almost complete inhibition of fMet-Leu-Phe and ionophore-induced cAMP responses in intact cells but had no effect on PGE1 and isoproterenol; 4) alpha 2-adrenergic agonists inhibited PGE1 but not chemoattractant- or A23187-elicited cAMP responses in intact PMNs; and 5) pretreatment of cells with a phosphodiesterase inhibitor (isobutylmethylxanthine) greatly potentiated the PGE1 and isoproterenol cAMP responses but nearly abolished the peak fMet-Leu-Phe response. Thus, chemoattractants appear to utilize a novel mechanism to raise cAMP levels which appear to require Ca2+ mobilization and could be mediated in part through a transient inhibition of phosphodiesterases. We suggest that stimulation of PMN functions by chemoattractants may utilize an N-coupled process to generate a Ca2+ signal which could in turn raise intracellular cAMP levels indirectly and thereby provide negative regulation.
Verghese
M W
MW
Fox
K
K
McPhail
L C
LC
Snyderman
R
R
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000527:Alprostadil; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D011458:Prostaglandins E / Q000494:pharmacology
D002147:Calmodulin; D011458:Prostaglandins E; D000001:Calcimycin; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D009240:N-Formylmethionine Leucyl-Phenylalanine; D005707:Gallic Acid; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D000527:Alprostadil; D007545:Isoproterenol; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine