Abstract
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 (EC(50) 65 nM) and sumatriptan (EC(50) 165 nM) activated GIRK channels in AtT20 cells expressing 5-HT(1B) receptors. Continuous application of both 5-HT (EC(50) 120 nM) and sumatriptan (EC(50) 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.