Regulation of Cyclic AMP Accumulation in Lymphoid Cells 1

Abstract

Abstract

We have examined several features of the regulation of cyclic AMP accumulation in lymphoid cells isolated from peripheral blood of human subjects and in the murine T-lymphoma cell line, S49. S49 cells are unique because of the availability of variant clones with lesions in the pathway of cyclic AMP generation and response. We found that human lymphoid cells prepared at 4°C showed substantially greater cyclic AMP accumulation in response to histamine and the β-adrenergic agonist isoproterenol than did cells prepared at ambient temperature. The muscarinic cholinergic agonist carbamylcholine and peptide hormone somatostatin failed to inhibit cyclic AMP accumulation in human lymphoid cells and treatment with pertussis toxin (which blocks function of G_i, the guanine nucleotide binding protein that mediates inhibition of adenylate cyclase) only minimally increased cyclic AMP levels in these cells. Thus the G_i component of adenylate cyclase appears to play only a small role in modulating cyclic AMP levels in this mixed population of lymphoid cells. Incubation of whole blood with isoproterenol desensitized human lymphocytes to subsequent stimulation with β agonist. This desensitization was associated with a redistribution of β-adrenergic receptors such that a substantial portion of the receptors in intact cells could no longer bind a hydrophilic antagonist. Wild-type S49 lymphoma cells showed a similar redistribution of β-adrenergic receptors after a few minutes'incubation with agonist. Based on studies in S49 variants, this redistribution is independent of components distal to receptors in the adenylate cyclase/cyclic AMP pathway. By contrast, a more slowly developing, agonist-mediated down-regulation of β-adrenergic receptors was blunted in variants with defective interaction between receptors and G_s, the guanine nucleotide binding protein that mediates stimulation of adenylate cyclase. Unlike results in human lymphoid cells, S49 cells show a prominent inhibition of cyclic AMP accumulation mediated by G_i; this inhibition is promoted by somatostatin and blocked by pertussis toxin.