title: Uptake of L-[propyl-2,3-3H]dihydroalprenolol by intact HeLa cells.
abstract: This report describes the uptake of L-[propyl-2,3-3H]dihydroalprenolol, a beta-adrenergic antagonist, by HeLa (human adenocarcinoma) cells. [3H]Dihydroalprenolol binds to sites of high capacity and low affinity in intact HeLa cells. The binding achieves equilibrium rapidly and is rapidly reversible. Bound [3H]dihydroalprenolol is displaceable by beta-adrenergic antagonists in a nonstereoselective fashion, but is not displaceable by isoproterenol, an adrenergic agonist. Phentolamine, an alpha-adrenergic antagonist, and chloroquine, a lysosomotropic amine, also compete for [3H]dihydroalprenolol binding sites. [3H]Dihydroalprenolol binding is inhibited by metabolic inhibitors, but not by cytoskeletal blocking agents. The binding is sensitive to extracellular pH (less binding at lower pH) and is temperature-sensitive (less binding at lower temperatures). The bound radioligand is rapidly reversed following hypotonic lysis of the cells. These [3H]dihydroalprenolol binding sites in intact HeLa cells therefore do not have the characteristics expected for beta-adrenergic receptors. Further studies showed that beta-adrenergic receptors could be detected in a HeLa membrane preparation using [125I]iodohydroxybenzylpindolol, and that chloroquine had very low affinity for these receptors. We conclude that [3H]dihydroalprenolol diffuses across the plasma membrane of intact HeLa cells and accumulates in acidic intracellular compartments.
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000526:Alprenolol / Q000031:analogs & derivatives*; D001667:Binding, Competitive; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002738:Chloroquine / Q000494:pharmacology; D003080:Cold Temperature; D004058:Diffusion; D004082:Dihydroalprenolol / Q000378:metabolism*; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D014634:Valinomycin; C011878:iodohydroxybenzylpindolol; D004082:Dihydroalprenolol; D000526:Alprenolol; D002738:Chloroquine; D010869:Pindolol; D007545:Isoproterenol; D010646:Phentolamine