Receptor Regulation of the Volume‐Sensitive Efflux of Taurine and Iodide from Human SH‐SY5Y Neuroblastoma Cells: Differential Requirements for Ca ²⁺ and Protein Kinase C

Muscarinic receptor regulation of osmosensitive taurine transport in human SH‐SY5Y neuroblastoma cells

“…To determine whether volume-dependent osmolyte efflux and uptake are coupled or independent events, the ability of DCPIB to prevent the inhibition of taurine uptake observed under conditions of hypotonicity and following mAChR activation was evaluated. As previously reported (Heacock et al 2006;Cheema et al 2007), pre-incubation of SH-SY5Y cells with 10 lM DCPIB completely prevented increases in taurine efflux observed under conditions of hypotonicity alone or following mAChR activation (Fig. 8a).…”

“…A common characteristic of those GPCRs that have been previously demonstrated to facilitate the efflux of osmolytes in SH-SY5Y cells is a dependence on both Ca 2+ availability and PKC activity. Similarly, the magnitude of the mAChRmediated reduction in taurine influx was also partially reversed (50-60%) following removal of extracellular Ca 2+ , although the dependence on Ca 2+ was less marked than that previously observed for stimulated taurine efflux (Cheema et al 2007). However, mAChR-mediated changes in taurine efflux and influx appeared to differ significantly in their dependence upon PKC activity.…”

“…The ability of mAChRs to facilitate osmosensitive taurine efflux is dependent upon both the availability of Ca 2+ and protein kinase C (PKC) activity. For example, under conditions of a limited Ca 2+ availability, mAChR-stimulated taurine efflux is inhibited by 60-81%, whereas inhibition of PKC with chelerythrine resulted in a 73% reduction in efflux (Cheema et al 2007). mAChR-mediated inhibition of taurine influx was also dependent upon Ca 2+ availability.…”

“…To minimize the contribution of taurine released from cells during measurements of taurine uptake, a 5 mL assay volume (25 nmol of added taurine) was routinely employed. From measurement of taurine contents in SH-SY5Y cells (see Results) and assuming a 20-30% release of taurine during a 10 min incubation under receptor-stimulated conditions (Heacock et al 2006;Cheema et al 2007), it can be calculated that the maximal contribution from release of endogenous taurine in each well is $3-4 nmol (a potential 11-14% reduction in specific activity). However, this value is likely to be an over-estimate as it assumes that taurine is released instantaneously from cells, whereas receptor-mediated efflux of taurine has been demonstrated to occur in a time-dependent manner during the 10 min incubation (Heacock et al 2006).…”