Abstract

The α7 nicotinic acetylcholine receptor subunit (CHRNA7) gene harbors a high degree of polymorphism. In this study, we found a novel variant (1267 G to A) in exon 10 of the CHRNA7 gene in a Japanese population. This variant results in glycine-to-serine substitution at position 423 (G423S) located in the large cytoplasmic loop of the protein. To clarify the possibility that the G423S mutation alters the pharmacological properties of α7 receptors, acetylcholine (ACh)-elicited current through α7-G423S mutant receptors expressed in Xenopus laevis oocytes was measured using the two-electrode voltage-clamp technique. We found that the current elicited by ACh (1 mM, 5 s) through α7-G423S receptors, but not through α7 receptors, was significantly decreased by treatment with a protein kinase C activator, phorbol-12-myristate-13-acetate (PMA, 10–30 nM). In addition, PMA (10 nM) selectively promoted a progressive decrease in α7-G423S current induced by repetitive application of ACh pulses (1 mM, 0.1 s, 0.17–0.33 Hz) compared with α7 current. PMA also enhanced the inactivation of α7-G423S mutant receptors induced by a prolonged application of choline (30 μM) without affecting α7 receptor responses. Western blot analysis showed that the treatment with PMA (30 nM) increased the serine phosphorylation level of the α7-G423S mutant receptors but not that of the wild-type receptors. These findings demonstrate that the G423S mutation promotes receptor desensitization by a protein kinase C-dependent mechanism. Thus, we provide the first evidence that a variant in the human CHRNA7 gene alters the function of α7 nicotinic receptors.