Figure 6. Chronic exposure to efavirenz reduces the 5-HT_2A receptor density and 5-HT mediated G_q activation at the 5-HT_2A receptor.

Cells were exposed (pretreated) for 3 days to DMSO vehicle [gray bars], serotonin (30 μM) [green bars] or efavirenz (30 μM) [blue bars], or to DMSO vehicle for 3 days and efavirenz for only 15 min on the third day [red bars]. The latter category was to ensure that our wash procedure was able to effectively remove all traces of efavirenz. After extensive washes, the cells from all groups were tested for their ability to mount functional responses to serotonin in the absence and presence of efavirenz (10 μM). All data were normalized to a maximal response generated by 100 μM 5-HT following the 3-day DMSO pretreatment and are presented as averaged values from multiple experiments ± SEM. A, Cells exposed to DMSO vehicle for 3 days elicited a robust calcium response when stimulated with a submaximal concentration of 5-HT (100 nM), and 10 μM efavirenz was able to antagonize this response by 48%. The same result was obtained when cells were exposed to efavirenz for only 15 min following 3 day exposure to DMSO, demonstrating that efavirenz could be easily removed by washing. Compared to the 3 day vehicle treated group, three day exposure to 30 μM 5-HT reduced the 100 μM maximal 5-HT response by 27%, and 10 μM efavirenz antagonized the 100 nM 5-HT submaximal response by 49%. In contrast to the other groups, 3 day exposure to 30 μM efavirenz drastically reduced the maximal 5-HT response by 81%, but the magnitude of efavirenz’s antagonist effect on the 100 nM 5-HT submaximal response was similar to all the other groups (i.e, a 49% reduction). The comparisons being made between specified groups within a category are indicated by interconnecting gray lines and show a significant inhibition by efavirenz. A bracket with asterisk indicates a significant difference between the 3 day DMSO category and the remaining categories for comparisons between matched groups. A two-way ANOVA followed by Bonferroni multiple comparisons test was performed to identify significant differences within and between the various pretreatment categories at P < 0.05. B, Three day exposure to 30 μM efavirenz resulted in a significant 52% decrease in receptor density (B_max). However, none of the other exposure conditions had a significant effect on B_max. A one way ANOVA followed by Bonferroni’s multiple comparisons test was performed to identify significant differences between various pretreatment categories. * P < 0.05 between the 3 day efavirenz pretreatment category and all the other pretreatment categories.