A novel mechanism for the inhibitory action of hydrocortisone at 5-HT3A receptors

NATALIA ANDERSEN; JEREMÍAS CORRADI; CECILIA BOUZAT

San Francisco, California

Congreso; 54th Biophysical Society Annual Meeting; 2010

Biophysical Society

The 5-HT3A receptor is a member of the Cys-loop family of ligand-gated ion channels. Due to its low conductance, analysis of this receptor has been restricted to the macroscopic level. We introduced mutations in the 5-HT3A subunit to obtain a high-conductance form so that single channels can be detected. We studied the actions of the neuroactive steroid, hydrocortisone (HC), in the high-conductance form of the 5-HT3A receptor. Channel activity elicited by 1 mM 5-HT appears as opening events of 4.6±0.4 pA (-70 mV) forming bursts, which coalesce into long clusters. A minor population of lower amplitude events (~2.7 pA) is observed, which corresponds to 0-10 % of the total events in all recordings. HC produces a concentration-dependent reduction in the duration of bursts and of the slowest open component (from ~100 to ~3.6 ms at 400 µM HC), which can be explained on the basis of a slow block mechanism. Interestingly, amplitude histograms reveal a concentration-dependent increase in the relative area of the low-amplitude component without changes in its mean value. At 400 mM HC, the low-amplitude events correspond to 40% of the total events. This channel population shows an amplitude of 2.8±0.5 pA (-70 mV). Macroscopic currents elicited by 5-HT in the presence of HC show reduced peak currents (~50% at 400 µM HC) and increased decay rates compared to those recorded in the absence of the steroid. Taken together, results reveal that hydrocortisone negatively modulates 5-HT3A receptors and show a novel mechanism which involves the stabilization of a sub-conductance form.