Thyrotropin-releasing hormone-induced spike and plateau in cytosolic free Ca2+ concentrations in pituitary cells. Relation to prolactin release.
1984; Elsevier BV; Volume: 259; Issue: 9 Linguagem: Inglês
10.1016/s0021-9258(18)91089-6
ISSN1083-351X
Autores Tópico(s)Stress Responses and Cortisol
ResumoUsing the acetoxymethyl ester of "Quin 2," a fluorescent Ca2+-indicator, we have loaded prolactin (PRL)producing rat pituitary cells with non-toxic concentrations of Quin 2 and quantitated changes in cytosolic free calcium concentration ([Ca2+]i) during stimulation of PRL release by thyrotropin-releasing hormone (TRH) and 40 mM K'.TRH induced a biphasic response, with an immediate (e1 s) spike in [Ca2+Ii from basal levels (350 2 80 nM) to a peak of 1-3 pM, which decayed rapidly (tl12 = 8 s) to a near basal nadir, then rising to a plateau in [Ca2+Ii of 500-800 nM.The TRHinduced spike phase was attenuated but not abolished by prior addition of EGTA, while the plateau phase was eliminated by EGTA.Addition of 40 mM K+ caused an immediate spike in [Ca2+Ii to 1-3 p~ which equilibrated slowly (tllz = 1 min) directly to a plateau of 600-800 nM.The K+-induced spike and plateau phases were both abolished by prior addition of EGTA.The biphasic nature of TRH action on [Ca2+]i parallels the biphasic actions of TRH on 46Ca2+ fluxes and the biphasic release of PRL by GH cells in suspension.These findings provide evidence that Ca2+-dependent agonist-mediated increases in [Ca2+Ii and hormone release are linked, and may generally have two modes: an acute "spike" mode, dependent primarily on redistribution of intracellular Ca2+ stores; and a sustained "plateau" mode, dependent on influx of extracellular Ca2+.That changes in cytosolic free calcium concentration ([Ca'+]J are coupled to the mechanism of secretion has been suggested in a wide variety of tissues (1-3).Yet rarely have changes in [Ca'+]; during stimulation of secretion been actually measured.We have used stimulation of PRL' release by TRH as a
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