The Influence of Monovalent Cations on Trimeric G Protein Gi1α Activity in HEK293 Cells Stably Expressing DOR-Gi1α (Cys351-Ile351) Fusion Protein

摘要

The effect of monovalent cations on trimeric G protein Gi1α was measured at equimolar concentration of chloride anion in pertussis-toxin (PTX)-treated HEK293 cells stably expressing PTXinsensitive DOR-Gi1α (Cys~(351)-Ile~(351)) fusion protein by high-affinity [35S]GTPγS binding assay. The high basal level of binding was detected in absence of DOR agonist and monovalent ions and this high level was inhibited with the order of: Na+ > K+ > Li+. The first significant inhibition was detected at 1 mM NaCl. The inhibition by monovalent ions was reversed by increasing concentrations of DOR agonist DADLE. The maximum DADLE response was also highest for sodium and decreased in the order of: Na~+ > K~+ ≈ Li~+. Our data indicate i) an inherently high activity of trimeric G protein Gi1α when expressed within DOR-Gi1α fusion protein and determined in the absence of monovalent cations, ii) preferential sensitivity of DOR-Gi1α to sodium as far as maximum of agonist response is involved.