Dependence of prolactin release on coupling between Ca(2+) mobilization and voltage-gated Ca(2+) influx pathways in rat lactotrophs |
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Authors: | Tomić Melanija Andric Silvna A Stojilkovic Stanko S |
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Affiliation: | (1) Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD |
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Abstract: | Two Ca2+-mobilizing receptors expressed in lactotrophs, endothelin-A (ETA) and thyrotropin-releasing hormone (TRH), induce a rapid Ca2+ release from intracellular stores and prolactin (PRL) secretion but differ in their actions during the sustained stimulation; TRH facilitates and ET-1 inhibits voltage-gated calcium influx (VGCI) and PRL secretion. In pertussis toxin (PTX)-treated cells, ET-1-induced inhibition of VGCI was abolished and the pattern of Ca2+ signaling was highly comparable with that observed in TRH-stimulated cells. The addition of Cs+, a relatively specific blocker of inward rectifier K+ channels, mimicked the effect of PTX on the pattern of ET-1-induced sustained Ca2+ signaling, but only in about 50% of cells, and did not affect agonist-induced inhibition of PRL secretion. Extracellular Cs+ was also ineffective in altering the TRH-induced facilitation of VGCI and PRL secretion. Furthermore, apamin and paxilline, specific blockers of Ca2+-activated SK-and BK-type K+ channels, respectively; E-4031, a blocker of ether a-go-go K+ channel; and linopirdine, a blocker of M-type K+ channel, did not affect the agonist-specific patterns of calcium signaling and PRL secretion. These results suggest that ET-1 inhibits VGCI through activation of Cs+-sensitive channels, presumably the Gi/o-controlled inward rectifier K+ channels, and that this agonist also inhibits PRL release, but downstream of Ca2+ influx. Further studies are required to identify the mechanism of sustained TRH-induced facilitation of VGCI and PRL secretion. |
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Keywords: | Endothelin-A thyrotropin-releasing hormone calcium prolactin voltage-gated calcium channels inward rectifier potassium channels |
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