Cyclic AMP counteracts mitogen-induced inositol phosphate generation and increases in intracellular Ca2+ concentrations in human lymphocytes.
1. The effects of increases in intracellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) on mitogen-induced generation of inositol phosphates and increases in intracellular Ca2+ concentration were investigated in human peripheral blood mononuclear leukocytes (MNL). 2. The mitogens concanavalin A (Con A), pokeweed mitogen (PWM) and phytohaemagglutinin (PHA) concentration-dependently stimulated generation of inositol phosphates. Catecholamines inhibited this process with an order of potency: isoprenaline greater than adrenaline greater than noradrenaline indicating involvement of beta 2-adrenoceptors. This order of potency was also consistent with the catecholamine potencies for stimulating the generation of cyclic AMP. 3. In addition to catecholamines, the cyclic AMP formation-stimulating agents prostaglandin E1 (PGE1) and forskolin concentration-dependently inhibited mitogen-induced inositol phosphate generation, too. Moreover, the inhibitory effect of isoprenaline was potentiated by co-incubation with the phosphodiesterase inhibitor isobutylmethylxanthine demonstrating that these inhibitory effects were mediated by cyclic AMP. 4. Con A and PHA concentration-dependently increased the intracellular Ca2+ concentration in human MNL (assessed by the fluorescent indicator dye Fura-2). This increase was almost completely blocked by chelation of extracellular Ca2+, demonstrating influx rather than mobilization from intracellular stores. 5. The elevation of intracellular Ca2+ was not blocked by pretreatment with pertussis toxin, 100 ng ml-1, for 16 h. 6. Isoprenaline, PGE1, and forskolin, however, inhibited the mitogen-stimulated elevation of intracellular Ca2+. This inhibition was enhanced by the phosphodiesterase inhibitors isobutylmethylxanthine and Ro 20-1724, demonstrating mediation by cyclic AMP. 7. We conclude that catecholamines and other cyclic AMP increasing agents can inhibit mitogen-stimulated generation of inositol phosphates and elevation of intracellular Ca2+ in resting human MNL.
van Tits
L J
LJ
Dept. Medicine, University of Essen, F.R.G.
Michel
M C
MC
Motulsky
H J
HJ
Maisel
A S
AS
Brodde
O E
OE
D000328:Adult; D000527:Alprostadil / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003208:Concanavalin A / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology*; D010835:Phytohemagglutinins / Q000494:pharmacology; D011043:Pokeweed Mitogens / Q000494:pharmacology
D002395:Catecholamines; D007295:Inositol Phosphates; D008934:Mitogens; D010835:Phytohemagglutinins; D011043:Pokeweed Mitogens; D003208:Concanavalin A; D005576:Colforsin; D000242:Cyclic AMP; D000527:Alprostadil; D007545:Isoproterenol; D002118:Calcium