title: Muscarinic receptor regulation of osmosensitive taurine transport in human SH-SY5Y neuroblastoma cells.
abstract: The ability of G protein-coupled receptors to regulate osmosensitive uptake of the organic osmolyte, taurine, into human SH-SY5Y neuroblastoma cells has been examined. When monitored under isotonic conditions and in the presence of physiologically relevant taurine concentrations (1-100 microM), taurine influx was mediated exclusively by a Na(+)-dependent, high-affinity (K(m) = 2.5 microM) saturable transport mechanism (V(max) = 0.087 nmol/mg protein/min). Reductions in osmolarity of > 20% (attained under conditions of a constant NaCl concentration) resulted in an inhibition of taurine influx (> 30%) that could be attributed to a reduction in V(max), whereas the K(m) for uptake remained unchanged. Inclusion of the muscarinic cholinergic agonist, oxotremorine-M (Oxo-M), also resulted in an attenuation of taurine influx (EC(50) approximately 0.7 microM). Although Oxo-M-mediated inhibition of taurine uptake could be observed under isotonic conditions (approximately 25-30%), the magnitude of inhibition was significantly enhanced by hypotonicity (approximately 55-60%), a result that also reflected a reduction in the V(max), but not the K(m), for taurine transport. Oxo-M-mediated inhibition of taurine uptake was dependent upon the availability of extracellular Ca(2+) but was independent of protein kinase C activity. In addition to Oxo-M, inclusion of either thrombin or sphingosine 1-phosphate also attenuated volume-dependent taurine uptake. The ability of Oxo-M to inhibit the influx of taurine was attenuated by 4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid, an inhibitor of the volume-sensitive organic osmolyte and anion channel. 4-[(2-Butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid also prevented receptor-mediated changes in the efflux and influx of K(+) under hypoosmotic conditions. The results suggest that muscarinic receptor activation can regulate both the volume-dependent efflux and uptake of taurine and that these events may be functionally coupled.
authors.affiliation: Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-2200, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Foster
authors.forename: Victor M
authors.initials: VM
authors.lastname: Vitvitsky
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
authors.forename: Anne M
authors.initials: AM
authors.lastname: Heacock
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Fisher
mesh_terms: D000409:Alanine / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D003517:Cyclopentanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019791:Guanidine / Q000494:pharmacology; D006801:Humans; D007189:Indans / Q000494:pharmacology; D008246:Lysophospholipids / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009447:Neuroblastoma; D009994:Osmolar Concentration; D010095:Oxotremorine / Q000031:analogs & derivatives; D011976:Receptors, Muscarinic / Q000502:physiology*; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013654:Taurine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D014316:Tritium / Q000378:metabolism / Q000494:pharmacology
chemical_list: C443139:4-(2-butyl-6,7-dichlor-2-cyclopentyl-indan-1-one-5-yl)oxybutyric acid; D000975:Antioxidants; D003517:Cyclopentanes; D004791:Enzyme Inhibitors; D007189:Indans; D008246:Lysophospholipids; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D012462:Saline Solution, Hypertonic; D014316:Tritium; D013654:Taurine; C060506:sphingosine 1-phosphate; C003949:hypotaurine; D010095:Oxotremorine; C042743:oxotremorine M; D019284:Thapsigargin; D013917:Thrombin; D019791:Guanidine; D013110:Sphingosine; D000409:Alanine; D002118:Calcium