Human 5-ht3 receptors: structural and functional features

MAZZARINI DIMARCO, A.; BOUZAT, C.B.; CORRADI, J.

Congreso; XXXV Reunión Anual Virtual de la Sociedad Argentina de Investigación en Neurociencias; 2020

The 5-HT3 receptor is a ligand-gated ion channel that converts the binding ofserotonin (5-HT) into a transient cation current which mediates fast excitatoryresponses in peripheral and central nervous systems. Five human subunits (AE) have been identified to date. The A subunit can assemble to form homomericreceptors (5-HT3A), or combine with B-E subunits to form heteromeric receptors(5-HT3AB-E). To determine subunit composition and stoichiometry of heteromericreceptors we constructed a high-conductance A subunit (AHC), which allowed usto detect single-channel events, and expressed the AHC with C, D or E subunits.From macroscopic currents we observed an increase in the 5-HT EC50 values forall subunit combinations with respect to that of 5-HT3AHC. Expression of the AHCto form 5-HT3AHC receptors showed opening events of homogeneous amplitudes.However, when AHC was expressed in combination with one of the C-E subunits,events with different amplitudes were detected, thus confirming the expression ofheteromeric receptors. In-silico studies provided insights into the contribution ofthe different subunits to the binding site conformation. Thus, our results confirmthat C-E subunits can combine with the A subunit to form heteromeric receptors,and bring structural and functional details about the different human 5-HT3receptors that can be expressed and expressed the AHC with C, D or E subunits. From macroscopic currents, we observed an increase in the 5-HT EC50 values for all subunit combinations with respect to that of 5-HT3AHC. Expression of the AHC to form 5-HT3AHC receptors showed opening events of homogeneous amplitudes. However, when AHC was expressed in combination with one of the C-E subunits, events with different amplitudes were detected, thus confirming the expression of heteromeric receptors. In-silico studies provided insights into the contribution of the different subunits to the binding site conformation. Thus, our results confirm that C-E subunits can combine with the A subunit to form heteromeric receptors, and bring structural and functional details about the different human 5-HT3 receptors that can be expressed.