Muscarinic Receptor Regulation of Osmosensitive Taurine Transport in Human SH-SY5Y Neuroblastoma Cells.
J Neurochem. 2008 Oct 8;
Authors: Foster DJ, Vitvitsky VM, Banerjee R, Heacock AM, Fisher SK
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 muM), taurine influx was mediated exclusively by a Na(+)-dependent, high-affinity (K(m)=2.5 muM) 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 muM). 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 (DCPIB), an inhibitor of the volume-sensitive organic osmolyte and anion channel. DCPIB 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.
PMID: 19012745 [PubMed - as supplied by publisher]