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Trh induced spike and plateau in cytosolic free calcium concentrations in pituitary cells relation to prolactin release


, : Trh induced spike and plateau in cytosolic free calcium concentrations in pituitary cells relation to prolactin release. Journal of Biological Chemistry 259(9): 5827-5832

Using the acetoxymethyl ester of Quin 2 a fluorescent CA2+-indicator, prolactin (PRL)-producing rat pituitary cells were loaded with non-toxic concentrations of Quin 2 and quantitated changes in cytosolic free calcium concentration ([Ca2+]i) during stimulation of PRL release by TRH and 40 mM K+. TRH induced a biphasic response, with an immediate (< 1 s) spike in [Ca2+]i from basal levels (350 .+-. 80 nM) to a peak of 1-3 .mu.M, which decayed rapidly (t1/2 = 8s) to a near basal nadir, then rising to a plateau in [Ca2+]i of 500-800 nM. The TRH-induced spike phase was attenuated but not abolished by prior addition of EGTA [ethylene glycol bis(.beta.-aminoethyl ether)-N,N,N',N'-tetraacetic acid], while the plateau phase was eliminated by EGTA. Addition of 40 mM K+ caused an immediate spike in [Ca2+]i to 1-3 .mu.M which equilibrated slowly (t1/2 = 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 45Ca2+ fluxes and the biphasic release of PRL by GH [growth hormone] cells in suspension. Ca2+-dependent agonist-mediated increases in [Ca2+]i and hormone release are linked, and may generally have 2 modes: an acute spike mode, dependent primarily on redistribution of intracellular Ca2+ stores; and a sustained plateau mode, dependent on influx of extracellular Ca2+.

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