Calbindin-D28k coexpression enhances cell surface expression of Ca²⁺ permeable AMPA receptors

Abstract

Recently, we reported that the expression of Ca²⁺ binding proteins, calbindin-D28k (CB) and parvalbumin correlates with the expression of Ca²⁺ permeable AMPA receptors(AMPA-Rs) in rat forebrain. We analyzed cell surface expression of a Ca²⁺ impermeable subunit, GluR2 and a Ca²⁺ permeable subunit, GluR2Q using an adenoviral-mediated expression system in COS7 cells. Biochemical measurements of cell surface expressed subunits using biotinylation experiments revealed that cell surface expression of GluR2Q is significantly increased with CB coexpression, while that of GluR2 is not. By application of AMPA-R blockers, cell surface expression of GluR2Q is increased in the absence of CB coexpression. This result suggests that the activity of AMPA-Rs formed by GluR2Q subunits suppresses cell surface expression of GluR2Q. To determine whether Ca²⁺ entry via Ca²⁺ permeable AMPA receptor causes the suppression, we used the Ca²⁺ chelater, BAPTA-AM. Application of BAPTA-AM increases cell surface expression of GluR2Q. These results suggest that CB enhances cell surface expression of Ca²⁺ permeable AMPA-Rs by buffering the increased intracellular Ca²⁺ that enters through Ca²⁺ permeable AMPA-Rs. [Jpn J Physiol 54 Suppl:S139 (2004)]