THE TM2-TM3 LOOP OF THE Α10 SUBUNIT IN THE POTENTIATION OF THE CHOLINERGIC NICOTINIC RECEPTOR Α9Α10 BY EXTRACELLULAR CALCIUM

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

Congreso; XXXIII Reunión Anual. de la. Sociedad Argentina de Investigación en Neurociencias; 2018

The α9α10 nicotinic acetylcholine receptor (nAChR) is expressed in cochlear hair cells. This nAChR mediates the inhibitory synapse between efferent fibers and outer hair cells. The inhibition results from calcium entry through the nAChR, in the presence of acetylcholine (ACh), followed by the activation of a Ca2+ dependent potassium current. This nAChR is composed of α9 and α10 subunits assembled into a pentameric cation-permeable ion channels. Each nAChR subunit comprises a large extracellular amino-terminal domain, four transmembrane domains (TM1-TM4) and a long cytoplasmic loop between TM3 and TM4. Expression of rat α9 and α10 nAChR subunits in Xenopus laevis oocytes yields functional α9 and α9α10 receptors, but not α10 homomeric nAChRs. One of the functional differences between α9 and α9α10 nAChRs is their modulation by extracellular Ca2+). α9 receptor responses to ACh are blocked by extracellular Ca2+. In contrast, α9α10 responses 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, expressed them in Xenopus oocytes 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 α9α10 nAChR by extracellular Ca2+.