ALPHA-2-ADRENERGIC RECEPTOR STIMULATION MOBILIZES INTRACELLULAR CA-2+ IN HUMAN ERYTHROLEUKEMIA-CELLS

  • 25 March 1989
    • journal article
    • research article
    • Vol. 264  (9) , 4986-4991
Abstract
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 protien-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.

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