Richman N H, Ford C A, Helms L M, Cooke I M, Pang P K, Grau E G
Department of Zoology, University of Hawaii, Honolulu 96822.
Gen Comp Endocrinol. 1991 Jul;83(1):56-67. doi: 10.1016/0016-6480(91)90105-f.
The relationship between tritium 3H-labeled prolactin (PRL) release and the loss of tissue-associated 45Ca2+ was examined in the tilapia rostral pars distalis (RPD) using perifusion incubation under conditions which inhibit or stimulate PRL release. Depolarizing [K+] (56 mM) and hyposmotic medium (280 mOsmolal) increased both the release of [3H]PRL and the loss of 45Ca2+. The responses to high [K+] were faster and shorter in duration than those produced by reduced osmotic pressure. The depletion of Ca2+ from the incubation medium with 2 mM EGTA suppressed the [3H]PRL response evoked by high [K+] or reduced osmotic pressure. Exposing the tissues to Ca(2+)-depleted medium in the absence of high [K+] or reduced osmotic pressure produced a sharp, but brief, increase in 45Ca2+ loss. Cobalt (10(-3) M), a competitive inhibitor of calcium-mediated processes, inhibited the [3H]PRL response to hyposmotic medium and to high [K+]. Cobalt also diminished the increased loss of 45Ca2+ evoked by exposure to reduced osmotic pressure, but was ineffective in altering responses to high [K+]. Methoxyverapamil (D600; 10(-5) M), a blocker of certain voltage-sensitive Ca2+ channels, did not alter either the [3H]PRL or the 45Ca2+ responses to high [K+] and reduced osmotic pressure. Taken together with our earlier studies, the present findings suggest that exposure to high [K+] or hyposmotic medium produces rapid changes in the Ca2+ metabolism of the tilapia RPD that are linked to the stimulation of PRL secretion. Nevertheless, the increased 45Ca2+ loss, but not [3H]PRL release, upon exposure to Ca(2+)-depleted media suggests that Ca2+ loss may not always reflect intracellular events that lead to PRL release.
利用灌流孵育法，在抑制或刺激催乳素（PRL）释放的条件下，研究了罗非鱼吻端垂体远侧部（RPD）中³H标记的催乳素释放与组织相关的⁴⁵Ca²⁺丢失之间的关系。去极化的[K⁺]（56 mM）和低渗培养基（280毫摩尔渗透压浓度）均可增加[³H]PRL的释放以及⁴⁵Ca²⁺的丢失。对高[K⁺]的反应比渗透压降低所产生的反应更快且持续时间更短。用2 mM乙二醇双四乙酸（EGTA）耗尽孵育培养基中的Ca²⁺，可抑制高[K⁺]或渗透压降低所诱发的[³H]PRL反应。在不存在高[K⁺]或渗透压降低的情况下，将组织暴露于Ca²⁺耗尽的培养基中，会导致⁴⁵Ca²⁺丢失急剧但短暂地增加。钴（10⁻³ M），一种钙介导过程的竞争性抑制剂，可抑制[³H]PRL对低渗培养基和高[K⁺]的反应。钴还减少了因暴露于渗透压降低环境所诱发的⁴⁵Ca²⁺丢失增加，但对改变对高[K⁺]的反应无效。甲氧基维拉帕米（D600；10⁻⁵ M），一种特定电压敏感性Ca²⁺通道的阻滞剂，不会改变[³H]PRL或⁴⁵Ca²⁺对高[K⁺]和渗透压降低的反应性。结合我们早期的研究，目前的研究结果表明，暴露于高[K⁺]或低渗培养基会使罗非鱼RPD的Ca²⁺代谢产生快速变化，这些变化与PRL分泌的刺激有关。然而，暴露于Ca²⁺耗尽的培养基时，⁴⁵Ca²⁺丢失增加，但[³H]PRL释放未增加，这表明Ca²⁺丢失可能并不总是反映导致PRL释放所需的细胞内事件。
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