Differential functional properties between homomeric and heteromeric 5-HT3 receptors

RODRIGUEZ ARAUJO, N.; BOUZAT, C.B.; MAZZARINI DIMARCO, A.; CORRADI, J.

Reunión Virtual

Congreso; XLIX Reunión Anual SAB; 2021

SAB - Sociedad Argentina de Biofísica

The serotonin type 3 receptor (5-HT3) is a ligand-gated ion channel that converts the binding of serotonin (5-HT) into a transient cation current and mediates fast excitatory responses in peripheral and central nervous systems. Five human subunits (A-E) have been identified to date. Only the A subunit can form homomeric receptors (5-HT3A). We performed single-channel and macroscopic current recordings from cells expressing different subunit combinations to determine how the accessory subunits contribute to the functional properties. The incorporation of the B subunit increases about 5-fold the EC50 value of 5-HT responses with respect to 5-HT3A receptors. At the single-channel level, 5HT3A receptors cannot be studied due to their reduced conductance. Thus, we also used a high-conductance A subunit (AHC) that forms openings of about 4.5 pA, which appeared grouped in long activation episodes of 287 ± 123 ms (-70 mV). The heteromeric AB channel has an amplitude of about 2 pA and activation episodes of markedly reduced durations compared to the homomeric (47,1 ± 4,4 ms). The pattern of channel activity did not show a clear concentration dependence for A and AB receptors. Also, both receptors were activated and potentiated by the allosteric agonist carvacrol. Expression of AHC with C, D or E subunits showed events with different amplitudes, indicating that A can assemble with one of these subunits. However, the frequency of channel activation was low, probably indicating that more complex subunit arrangements may occur. In-silico studies provided insights into the contribution of the different subunits to the binding site. Our results provide basis for identifying functional heteromeric receptors in native cells and for understanding their distinct roles; and opens doors for the development of specific ligands.