Abstract
Expressed metabotropic group 1 glutamate mGluR5 receptors and nucleotide P2Y1 receptors (P2Y1Rs) show promiscuous ion channel coupling in sympathetic neurons: their stimulation inhibits M-type [Kv7, K(M)] potassium currents and N-type (Ca(V)2.2) calcium currents (Kammermeier and Ikeda, 1999; Brown et al., 2000). These effects are mediated by G(q) and G(i/o) G-proteins, respectively. Via their C-terminal tetrapeptide, these receptors also bind to the PDZ domain of the scaffold protein NHERF2, which enhances their coupling to G(q)-mediated Ca(2+) signaling (Fam et al., 2005; Paquet et al., 2006b). We investigated whether NHERF2 could modulate coupling to neuronal ion channels. We find that coexpression of NHERF2 in sympathetic neurons (by intranuclear cDNA injections) does not affect the extent of M-type potassium current inhibition produced by either receptor but strongly reduced Ca(V)2.2 inhibition by both P2Y1R and mGluR5 activation. NHERF2 expression had no significant effect on Ca(V)2.2 inhibition by norepinephrine (via alpha(2)-adrenoceptors, which do not bind NHERF2), nor on Ca(V)2.2 inhibition produced by an expressed P2Y1R lacking the NHERF2-binding DTSL motif. Thus, NHERF2 selectively restricts downstream coupling of mGluR5 and P2Y1Rs in neurons to G(q)-mediated responses such as M-current inhibition. Differential distribution of NHERF2 in neurons may therefore determine coupling of mGluR5 receptors and P2Y1 receptors to calcium channels.