Differences between human wild-type and C23S variant 5-HT2C receptors in inverse agonist-induced resensitization

• Published in: Pharmacological reports 2011-01, Vol.63 (1), p.45-53
• Main Authors: Walstab, Jutta, Steinhagen, Folkert, Brüss, Michael, Göthert, Manfred, Bönisch, Heinz
• Format: Article
• Language: English
• Subjects: 5-HT2c receptor; Adult; aequorin; Aequorin - chemistry; Base Sequence; C23S variant; calcium; Calcium - metabolism; DNA, Complementary - chemistry; Drug Inverse Agonism; Drug Safety and Pharmacovigilance; Ergolines - metabolism; HEK293 Cells; Humans; Indoles - pharmacology; inverse agonist; Luminescent Measurements - methods; Pharmacotherapy; Pharmacy; Protein Binding; Pyridines - pharmacology; receptor desensitization; Receptor, Serotonin, 5-HT2C - drug effects; Receptor, Serotonin, 5-HT2C - genetics; Receptor, Serotonin, 5-HT2C - metabolism; SB 206553; Serotonin - administration & dosage; Serotonin - pharmacology; Serotonin Antagonists - metabolism; Serotonin Antagonists - pharmacology; Time Factors
• ISSN: 1734-1140; 2299-5684
• DOI: 10.1016/S1734-1140(11)70397-8

The aim of this study was to analyze functional properties of the naturally occurring C23S variant of the human 5-HT2C receptor. In HEK293 cells transiently expressing the unedited forms of the variant receptor (VR) or the wild-type receptor (WTR), surface expression was determined by [3H]mesulergine binding to membrane fragments. Function was examined by an aequorin luminescence-based Ca2+ assay. Surface expression of the VR was 116% of that of the WTR. The 5-HT-induced increase in cytosolic Ca2+ ([Ca2+]i), and its inhibition by the inverse agonist SB 206553 did not differ between VR- or WTR-expressing cells. Preexposure of VR- or WTR-expressing cells to 0.5µM 5-HT (3min–4.5h) led to a practically identical time course and extent in the reduction of the 5-HT-induced increase in [Ca2+];. In contrast, prolonged preexposure to the inverse agonist SB 206553 (1µM) elevated the 5-HT-induced increase in [Ca2+]i for both isoreceptors. A preexposure time of 4.5h was necessary to significantly elevate the Ca2+ response of the WTR, but the VR produced this elevation within 1h with virtually no further effect after 4.5h of preexposure. In conclusion, prolonged preexposure to 5-HT caused equally rapid and strong desensitization of both isoreceptors. The different time course of SB 206553-induced resensitization of the two isoreceptors might be therapeutically relevant for drugs exhibiting inverse agonist properties at 5-HT2C receptors, such as atypical antipsychotics and certain antidepressants.