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Potentiation of prolactin secretion following lactotrope escape from dopamine action. I. Dopamine withdrawal augments l-type calcium current.

Abstract：

:Hypothalamic dopamine (DA) tonically inhibits prolactin (PRL) release from the anterior pituitary gland. Transient escapes from this DA tone elicit a pronounced potentiation of the PRL-releasing action of secretagogues such as thyrotropin-releasing hormone (TRH). Previous evidence has suggested that modulation of Ca(2+) channels can be involved in this potentiation. With a lactotropic cell line (GH(4)C(1)) expressing human D(2)-DA receptors, we tested the hypothesis that a brief escape from the tonic inhibitory action of DA triggers a facilitation of Ca(2+) influx through Ca(2+) channels. We initially found that in these cells, DA effectively and reversibly inhibited PRL secretion, and reversibly enhanced an inwardly rectifying K(+) current. The effects of DA administration and withdrawal on Ca(2+) currents were examined using the patch-clamp technique in the whole-cell configuration and Ba(2+) as a divalent charge carrier through Ca(2+) channels. Macroscopic Ba(2+) currents were significantly decreased by short term (1-10 min) applications of DA (500 nM), which further declined following 24 h of constant exposure to DA. After DA removal, a biphasic facilitation of the density of Ba(2+) currents was observed. An initial 2-fold enhancement of conductance was detected between 10 and 40 min, followed by a second facilitation of the same magnitude observed 24 h after DA withdrawal. The present results directly demonstrate that dissociation of DA from D(2)-receptors expressed in GH(4)C(1) lactotrope cells causes an increase of high-voltage-activated Ca(2+) channel function, which may play an important role in the cross-talking amplification of endocrine cascades such as that involved in the TRH-induced PRL-release potentiating action of DA withdrawal.

journal_name

Neuroendocrinology

journal_title

Neuroendocrinology

authors

del Mar Hernández M,García Ferreiro RE,García DE,Hernández ME,Clapp C,Martínez de la Escalera G

doi

10.1159/000054456

subject

Has Abstract

pub_date

1999-07-01 00:00:00

pages

20-30

issue

eissn

0028-3835

issn

1423-0194

pii

54456

journal_volume

pub_type

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Potentiation of prolactin secretion following lactotrope escape from dopamine action. I. Dopamine withdrawal augments l-type calcium current.