Modulation of dopamine (DA) receptors by cations (Na+, K+, Mg2+, Ca2+) was compared in 7315a, MtTW15, and estradiol valerate-induced (EV-T) pituitary tumors, and intact adenohypophysis. In 7315a tumors, the affinity of [3H]spiperone binding measured at 25 degrees remained unchanged in the presence of each cation individually or all these cations together (IONS) compared to the affinity obtained using a buffer without ions; the density (Bmax) was not affected by monovalent cations or Mg2+ and was decreased by Ca2+ or IONS. When binding experiments were done at 37 degrees, monovalent cations increased affinity whereas divalent cations or IONS did not modify it, and none of these cations affected Bmax values. In MtTW15 tumors, the affinity of [3H]spiperone binding measured at 25 degrees was not changed by Na+ or IONS and was decreased by K+ or divalent cations; the density was decreased by K+ and unchanged by all the other cations. When binding experiments were done at 37 degrees, Na+ increased the affinity, whereas all the other cations did not affect it: the density was unaffected by all the cations studied. In EV-T assayed at 37 degrees, the affinity was increased by monovalent cations or Mg2+ and was unchanged by Ca2+; monovalent cations did not affect the density of [3H]spiperone binding and divalent cations increased it. In binding experiments performed at 25 degrees and 37 degrees, choline chloride did not change the affinity or the density of [3H]spiperone binding to DA receptors in the three pituitary tumors investigated, suggesting that the effect of cations was specific and not due to differences in ionic strength. In the rat normal anterior pituitary, Na+ increased the affinity of [3H]spiperone for the DA receptors, whereas the affinity was unchanged by Ca2+; the density of [3H]spiperone binding was unaffected by these cations. Our results suggest that DA receptors in 7315a and MtTW15 tumors are regulated abnormally by sodium, potassium, magnesium and calcium. In contrast, DA receptors in EV-T are regulated normally by monovalent cations and abnormally by divalent cations as compared to these receptors in intact pituitary tissue.

译文

在7315a,MtTW15和戊酸雌二醇诱发的垂体瘤(EV-T)和完整的腺垂体中比较了阳离子(Na,K,Mg2,Ca2)对多巴胺(DA)受体的调节作用。在7315a肿瘤中,与使用无离子缓冲液获得的亲和力相比,在每个阳离子单独存在或所有这些阳离子在一起(IONS)的情况下,在25度下测得的[3H]哌酮结合的亲和力保持不变。密度(Bmax)不受单价阳离子或Mg2影响,而受Ca2或IONS降低。当在37度下进行结合实验时,单价阳离子增加了亲和力,而二价阳离子或IONS却没有对其进行修饰,并且这些阳离子都没有影响Bmax值。在MtTW15肿瘤中,在25度测量的[3H]哌咯酮结合的亲和力没有被Na或IONS改变,而被K或二价阳离子降低了。密度降低了K,而所有其他阳离子均未改变。当在37度下进行结合实验时,Na增加了亲和力,而所有其他阳离子均不影响它:密度不受所有研究阳离子的影响。在37度的EV-T中,单价阳离子或Mg2增加了亲和力,而Ca2没有改变亲和力。一价阳离子不影响[3H]哌咯酮结合的密度,而二价阳离子则增加了它的密度。在25度和37度进行的结合实验中,氯化胆碱并未改变所研究的三个垂体肿瘤中[3H]哌咯酮与DA受体的亲和力或密度,这表明阳离子的作用是特异性的,而不是由于差异离子强度。在大鼠正常的垂体前叶,Na增加了[3H] spiperone对DA受体的亲和力,而Ca2却没有改变亲和力。 [3H] spiperone结合的密度不受这些阳离子的影响。我们的结果表明,钠,钾,镁和钙异常调节7315a和MtTW15肿瘤中的DA受体。相反,与完整的垂体组织中的这些受体相比,EV-T中的DA受体通常由单价阳离子调节,而由二价阳离子异常调节。

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