Regulation Of The Molecular Function Of Α7 Nicotinic Receptor By Phosphorylation

Abstract

α7 is one of the most abundant nicotinic receptors in the nervous system. It is highly expressed in the brain and contributes to cognition, attention, and working memory. The receptor contains an extracellular domain, which carries the agonist binding sites; a transmembrane domain, which forms the ion pore and the gate; and an intracellular domain (ICD), which contains sites for modulation and intracellular signaling. The concept of α7 as a dual metabotropic/ionotropic receptor is attracting increasing attention. Reciprocal crosstalk between phosphorylation-dependent signaling and receptor function has been proposed. However, the regulation of ion channel function by phosphorylation remains unclear. We here explored how tyrosine phosphorylation at ICD affects single-channel function of human α7 by combining site-directed mutagenesis and mammalian cell expression with patch-clamp recordings. We generated two mutant α7 receptors to prevent phosphorylation of key tyrosine residues (α7Y386F and α7Y442F). Wild-type α7 channel activity elicited by ACh consists of brief and isolated openings and less often as few brief openings in quick succession (bursts). We found that the mutations do not affect single-channel amplitude. However, visual inspection of the recordings showed sporadically long-duration bursts that were not detected in the wild-type receptor. To quantify these differences, we analyzed the burst duration histograms. Whereas wild-type α7 histograms are fitted by 2 components, about 40% of the recordings of α7Y386F and 20% of α7Y442F show a third component. This component corresponds to a novel population of long-duration bursts. Our results show that the decrease of phosphorylation increases open-channel duration, probably by reducing fast desensitization, which is the main pathway for terminating an opening event in α7.These findings reveal a novel regulatory mechanism that may be important in receptor function.