ANALYSIS OF THE STRUCTURAL DETERMINANTS RESPONSIBLE FOR THE POTENTIATION OF THE CHOLINERGIC NICOTINIC RECEPTOR ALPHA9 ALPHA10 BY EXTRACELLULAR CALCIUM

SOFIA GALLINO; PAOLA PLAZAS; JUAN CARLOS BOFFI; ANA BELÉN ELGOYHEN

Congreso; Fronteras en Biociencia 3; 2018

Nicotinic cholinergic receptors (nAChR) are pentameric cation-permeable ion channels activated by acetylcholine (ACh). Each nAChR subunit comprises a large extracellular amino-terminal domain, four transmembrane domains (TM1-TM4) and a long cytoplasmic loop between TM3 and TM4. The 910 nAChR mediates synaptic transmission between olivocochlear fibers and outer hair cells of the cochlea. cRNA expression of rat 9 and 10 nAChR subunits in Xenopus laevis oocytes yields functional α9 and 910 receptors, but not α10 homomeric nAChRs. One of the functional differences between α9 and 910 nAChRs is the modulation of their ACh-evoked responses by extracellular calcium (Ca2+). While 9 nAChRs responses to ACh are blocked by extracellular Ca2+. In contrast, ACh-evoked currents through 910 nAChRs responses to ACh are potentiated at sub-mM Ca2+ concentrations and blocked by higher concentrations of this ion. In order to determine the structural determinants responsible for these differences, we generated chimeric subunits, exchanging domains between a9 and a10 subunits, expressed them in Xenopus oocyes and performed electrophysiological recordings under two electrode voltage clamp. Our results suggest that the TM2- TM3 loop of the α10 subunit contains key structural determinants responsible for the potentiation of the 910 nAChR by extracellular Ca2+.