Regulation of heterologously expressed 5-HT_1B receptors coupling to potassium channels in AtT-20 cells

Background and purpose: 5-HT_1B receptors are widely expressed GPCRs and a target of triptans, the most commonly prescribed anti-migraine drugs. There is very limited information about the acute, agonist-induced regulation of 5-HT_1B receptor signalling and so we sought to characterize this in a neuron-like system.

Experimental approach: Epitope-tagged human 5-HT_1B receptors were expressed in mouse AtT20 cells. 5-HT_1B receptor signalling was assessed using whole-cell patch-clamp recordings of endogenous G protein-gated inwardly rectified potassium (GIRK) channels, and receptor localization measured using immunofluorescence.

Key results: 5-HT (EC₅₀ 65 nM) and sumatriptan (EC₅₀ 165 nM) activated GIRK channels in AtT20 cells expressing 5-HT_1B receptors. Continuous application of both 5-HT (EC₅₀ 120 nM) and sumatriptan (EC₅₀ 280 nM) produced profound desensitization of 5-HT_1B receptor signalling within a few minutes. Complete recovery from desensitization was observed after 10 min. Both 5-HT and sumatriptan induced significant heterologous desensitization of SRIF (somatostatin)-activated GIRK currents, with the 5-HT-induced heterologous desensitization being blocked by the protein kinase inhibitor staurosporine. Both agonists induced modest 5-HT_1B receptor internalization, with a time course much slower than receptor desensitization.

Conclusions and implications: In AtT-20 cells, 5-HT_1B receptors undergo rapid and reversible desensitization at concentrations of agonist similar to those required to activate the receptor. Desensitization is incomplete, and the continued signalling of the receptor in the presence of the agonist may lead to cellular adaptations. Finally, 5-HT_1B receptor activation causes significant heterologous desensitization, which may lead to a reduced effectiveness of unrelated drugs in vivo.