Identification of a novel regulatory mechanism for norepinephrine transporter activity by the IP3 receptor

The norepinephrine transporter (NET) plays a crucial role in noradrenergic neurotransmission and is a target of many antidepressants and psychostimulants. Intracellular Ca2+ is reportedly involved in regulating NET activity, but the detailed mechanism is not clear. We employed a norepinephrine uptake assay using SH-SY5Y cells and found that the IP3 receptor inhibitors, 2-aminoethoxydiphenyl borate and xestospongin C, reduced the NET Vmax. These reductions were accompanied by the decreased cell surface expression of NET. Our findings suggest that intracellular Ca2+ mobilized by IP3 receptor is required for the maintenance of NET activity. This adds another pathway involving Ca2+ for the regulation of NET to other known mechanisms providing intracellular Ca2+.