Activation of 5-hydroxytryptamine4 receptors causes calcium influx in adrenocortical cells: involvement of calcium in 5-hydroxytryptamine-induced steroid secretion
Contesse, V.; Hamel, C.; Lefebvre, H.; Dumuis, A.; Vaudry, H.; Delarue, C.
Molecular Pharmacology 49(3): 481-493
1996
ISSN/ISBN: 0026-895X PMID: 8643088 Document Number: 464197
5-Hydroxytryptamine (5-HT) stimulates corticosteroid secretion from adrenal cells through activation of 5-HT, receptors positively coupled to adenylyl-cyclase. In the present study, we investigated in frog adrenocortical cells the effect of 5-HT-4 receptor agonists on cytosolic calcium concentration ((Ca-2+)-i) and determined the sequence of events associated with 5-HT-4 receptor activation. The application of 5-HT or the 5-HT-4 receptor agonist zacopride (10-8 to 10-5 m each) in the vicinity of cultured adrenocortical cells caused a dose-dependent increase in (Ca-2+). Preincubation of the cells with the selective 5-HT-4 receptor antagonist (1-(2-(methylsulfonylamino)ethyl)-4-piperidinyl)-methyl-1-methyl-1H-indole-3-carboxylate maleate totally blocked the 5-HT-induced stimulation of (Ca-2+)-i. Chelation of extracellular calcium with ethylene glycol bis(O-aminoethyl ether)-N,N,N',N'-tetraacetic acid (10 mm) suppressed the stimulatory effect of 5-HT on (Ca-2+)-i. Conversely, thapsigargin, an inhibitor of calcium ATPase activity, had no effect on the (Ca-2+)-i rise. The calcium influx induced by 5-HT, receptor agonists was not affected by nifedipine and omega-conotoxin GVIA but was totally blocked by pimozide, a T-type calcium channel antagonist. The (Ca-2+)-i response to zacopride was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1 -methylxanthine and markedly reduced by the protein kinase A inhibitor adenosine-3',5'-cyclic monophosphorothioate. We studied in perifused frog adrenal slices the involvement of (Ca-2+)-i rise and cAMP formation in the mechanism of action of 5-HT-4 receptor agonists. Zacopride-induced steroidogenesis was significantly reduced in the presence of adenosine-3',5'-cyclic monophosphorothioate or after suppression of calcium in the perfusion medium. The stimulatory effect of zacopride on corticosteroid secretion was not affected by nifedipine and omega-conotoxin GVIA but was significantly inhibited by pimozide. Taken together, these data indicate that activation of 5-HT-4 receptors in adrenocortical cells causes stimulation of adenylyl cyclase and subsequently increases calcium influx through a T-type calcium channel. Both the increased in cAMP formation and the calcium rise are involved in the stimulatory effect of 5-HT on corticosteroid secretion.