Abstract
5-HT3 receptors cloned from NCB-20 cells were expressed in Xenopus oocytes, and the effects of forskolin and steroids on the function of the receptors were investigated using the two-electrode voltage-clamp technique. Forskolin, 17-β-estradiol, and progesterone inhibited the currents activated by 1 μM 5-HT in a reversible and concentration-dependent manner, with IC50 values of 12, 33, and 89 μM, respectively. The inhibitory effects of forskolin and 17-β-estradiol were independent of the membrane potential. Forskolin and 17-β-estradiol significantly reduced the maximal amplitude of the 5-HT concentration-response curve (Emax) without significantly affecting the EC50, indicating that these compounds act as noncompetitive inhibitors of the 5-HT3 receptor. The cAMP analogue, 8-Br-cAMP (0.2mM), and the protein kinase A activator, Sp-cAMP (0.1 mM), did not affect the amplitude of 5-HT3 receptor-mediated currents. The membrane-permeable protein kinase A inhibitor Rp-cAMP (0.1 mM) and the estrogen-receptor antagonist tamoxifen (1 μM) did not affect the inhibition of 5-HT-activated current. In addition, 5-HT3 receptor-mediated currents were inhibited by both 1,9-dideoxy forskolin (30 μM), which does not activate adenylyl cyclase, and wForskolin (30 μM), a charged hydrophilic analogue of forskolin that is membrane impermeable. These results indicate that both forskolin and 17-β3-estradiol inhibit the function of the 5-HT3 receptor in a noncompetitive manner and that this inhibition is independent of cAMP levels.
Original language | English |
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Pages (from-to) | 293-301 |
Number of pages | 9 |
Journal | Archives of Biochemistry and Biophysics |
Volume | 404 |
Issue number | 2 |
DOIs | |
Publication status | Published - Aug 15 2002 |
Externally published | Yes |
Keywords
- 5-HT receptor
- CyclicAMP
- Forskolin
- Steroids
- Xenopus oocyte
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Molecular Biology