Characterization of 5-HT2A receptor desensitization and the effect of cycloheximide on it in C6 cells

Effect of prolonged pretreatment with serotonin (5-HT) on 5-HT2A receptor d esensitization was examined by the measurement of intracellular calcium ([C a2+](i)) mobilization in C6 cells. 5-HT-induced desensitization of [Ca2+](i ) mobilization was in a time and dose dependent manner and reached a platea u after 3 hr. After 1 and 3 hr 5-HT pretreatment, 5-HT concentration in the medium little changed. 5-HT pretreatment with cycloheximide, a protein syn thesis inhibitor, produced an enhancement of the desensitization for 3 and 6 hr pretreatment. However, 5-HT pretreatment for 3 and 6 hr caused no mark ed change in the 5-HT2A receptor mRNA level or G alphaq/11 protein in this study, suggesting that 5-HT may decrease 5-HT-induced [Ca2+](i) mobilizatio n independent of 5-HT2A receptor mRNA or G-proteins. Endothelin-l-induced [ Ca2+](i) mobilization did not alter after 5-HT and/or cycloheximide pretrea tment. These results showed that activation of the 5-HT2A receptor induced homologous desensitization and pretreatment with 5-HT and/or cycloheximide did not change the efficacy of the second messenger pathway from Gq to a [C a2+](i) rise.