Presence of a 5-HT7 receptor positively coupled to adenylate cyclase activation in human granulosa-lutein cells

Although serotonin (5-HT) has been shown to stimulate progesterone production by human granulosa-lutein cells (hGLC), the receptor type and associated signaling pathway remain uncharacterized. We report here that 5-HT receptors in these cells are positively coupled to adenylate cyclase activity. Formation of cAMP was stimulated by 5-HT and its agonists in a dose- and time-dependent manner. Mianserin, amoxapine, and loxapine were equipotent in antagonizing 5-HT-induced cAMP formation. For both cAMP formation in cells and adenylate cyclase assay using membrane fractions, the rank order of potency for agonists of 5-HT were: 5-carboxy-aminotryptamine >5-HT> or =5-methoxytryptamine, consistent with a typical kpharmacological profile of human 5-ht(7) (h5-ht(7)) receptor. Sequence data of amplified complementary DNA fragments reverse transcribed from hGLC RNA revealed complete identity with published sequence of h5-ht(7) receptor complementary DNA. Northern analysis showed the presence of 2.8-kb h5-ht(7) transcripts in hGLC. The three variants h5-ht(7A) h5-ht(7B), and h5-ht(7D) were also detected in hGLC. Preincubation of hGLC with 5-HT (10(-8)-10(-6) M) resulted in a marked reduction in the cAMP response when the cells were subsequently stimulated with gonadotropin, and this heterologous desensitization could be reversed by 5-ht(7) receptor antagonist clozapine. These data demonstrate that h5-ht(7) receptor is present and stimulate cAMP formation in hGLC. In addition, the h5-ht(7) receptor seems to be implicated in the heterologous down-regulation hCG-stimulated cAMP response in hGLC, with a possible ramification for luteal insufficiency.