Activation of 5-HT7 Receptor in Rat Glomerulosa Cells Is Associated with an Increase in Adenylyl Cyclase Activity and Calcium Influx through T-Type Calcium Channels
Serotonin (5-HT) stimulates aldosterone secretion from the rat adrenal gland through 5-HT7 receptors. The aim of the present study was to investigate the transduction mecha- nisms associated with activation of 5-HT7 receptors in rat glomerulosa cells. The stimulatory effect of 5-HT on aldoste- rone secretion and cAMP formation was significantly reduced by the 5-HT7 receptor antagonist LY 215840. Pretreatment of cells with the adenylyl cyclase inhibitor SQ 22536 or the PKA inhibitor H-89 markedly attenuated the effect of 5-HT on al- dosterone secretion. Conversely, type 2 and 4 phosphodies- terase inhibitors potentiated the 5-HT-induced stimulation of aldosterone secretion. Administration of 5-HT in the vicinity of cultured glomerulosa cells induced a slowly developing and robust increase in cytosolic calcium concentration ((Ca2)i). The effect of 5-HT on (Ca2)i was suppressed by mibefradil, a T-type calcium channel blocker. Patch-clamp studies con- firmed that 5-HT activated a T-type calcium current. Mibe- fradil also induced a dose-dependent inhibition of 5-HT- induced aldosterone secretion. The sequence of events asso- ciated with activation of 5-HT7 receptors was investigated. The PKA inhibitor H-89 markedly attenuated both the (Ca2)i response and the activation of T-type calcium current induced by 5-HT. In contrast, reduction of the calcium concentration in the incubation medium did not affect 5-HT- induced cAMP formation. Preincubation of glomerulosa cells with cholera toxin abolished the stimulatory effect of 5-HT on aldosterone secretion, but pertussis toxin had no effect. Taken together, these data demonstrate that, in rat glomerulosa cells, activa- tion of native 5-HT7 receptors stimulates cAMP formation through a Gs protein, which in turn provokes calcium influx through T-type calcium channels. Both the adenylyl cyclase/ PKA pathway and the calcium influx are involved in 5-HT- induced aldosterone secretion. (Endocrinology 143: 1748-1760, 2002)