Alpha 2-adrenergic receptor stimulation mobilizes intracellular Ca2+ in human erythroleukemia cells.
Human erythroleukemia cells are a model system for studies of alpha 2-adrenergic receptors and their coupling to inhibition of adenylate cyclase (McKernan, R. M., Howard, M. J., Motulsky, H. J., and Insel, P. A. (1987) Mol. Pharmacol. 32, 258-265). Using Fura-2, we show that alpha 2-adrenergic receptor stimulation also increases intracellular Ca2+ in these cells by 80-250 nM. Although epinephrine only inhibited forskolin-stimulated cAMP generation when beta-adrenergic receptors were blocked, the Ca2+ increase was not affected by beta-adrenergic receptor blockade. The Ca2+ increase was not affected by forskolin or 8-bromo-cAMP. Thus, alpha 2-adrenergic receptors independently couple to elevation of intracellular Ca2+ and adenylate cyclase inhibition. Chelating all extracellular Ca2+ did not reduce the response, demonstrating mobilization of intracellular, rather than influx of extracellular Ca2+. The epinephrine-stimulated Ca2+ mobilization occurred prior to any detectable increase in inositol-(1,4,5)-trisphosphate. It was abolished by pretreatment with pertussis toxin (which blocks some G protein-mediated processes), but not by aspirin and indomethacin (which inhibit cyclooxygenase), nordihydroguaiaretic acid (which inhibits lipoxygenase), or Na+-free buffer (to block any Na+H+ exchange). We conclude, therefore, that alpha 2-adrenergic receptors on human erythroleukemia cells couple to mobilization of intracellular Ca2+ via a (pertussis toxin-sensitive) G protein-mediated mechanism that is independent of inhibition of adenylate cyclase.
Michel
M C
MC
Department of Pharmacology, University of California, San Diego, La Jolla 92093.
Brass
L F
LF
Williams
A
A
Bokoch
G M
GM
LaMorte
V J
VJ
Motulsky
H J
HJ
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers
D000316:Adrenergic alpha-Agonists; D002352:Carrier Proteins; D007295:Inositol Phosphates; D011942:Receptors, Adrenergic, alpha; D017923:Sodium-Hydrogen Exchangers; D000242:Cyclic AMP; D006152:Cyclic GMP; D002118:Calcium