Regulation of heterologously expressed 5-HT1B receptors coupling to potassium channels in AtT-20 cells.

Abstract

5-HT1B 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-HT1B receptor signalling and so we sought to characterize this in a neuron-like system. Epitope-tagged human 5-HT1B receptors were expressed in mouse AtT20 cells. 5-HT1B 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. 5-HT (EC50 65nM) and sumatriptan (EC50 165nM) activated GIRK channels in AtT20 cells expressing 5-HT1B receptors. Continuous application of both 5-HT (EC50 120nM) and sumatriptan (EC50 280nM) produced profound desensitization of 5-HT1B receptor signalling within a few minutes. Complete recovery from desensitization was observed after 10min. 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-HT1B receptor internalization, with a time course much slower than receptor desensitization. In AtT-20 cells, 5-HT1B 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-HT1B receptor activation causes significant heterologous desensitization, which may lead to a reduced effectiveness of unrelated drugs in vivo.