Palmer K C, Grammas P
Lab Invest. 1987 Mar;56(3):329-34.
Ethylnitrosourea-induced pulmonary adenomas of the mouse have been reported as being predominantly Clara cell in origin. The response of these tumor cells in vivo to the secretory agonist, isoproterenol (10 mg/kg) and the antagonist, propranolol (2.0 mg/kg) 1 hour after intraperitoneal injection into 120-day-old tumor-bearing mice was examined. Ultrastructural morphometry was used to quantitate the secretory response of tumor cells by measuring the volume density of the secretory granules. In the intact animal, isoproterenol stimulated secretion in the Clara cell adenomas (40% decrease in volume density with no change in surface to volume ratio of granules), while propranolol prevented this effect. In addition, beta-adrenergic receptors on isolated tumor cells were demonstrated by radioligand-binding assay by using [125I]iodocyanopindolol (ICYP). Scatchard analysis of data derived from whole cells indicates a maximum receptor-binding capacity of 27 fmoles/mg of protein and a KD of 0.029 nM. Isoproterenol displacement of ICYP binding yields an IC50 of 8 X 10(-7) M and a calculated KD of 3.36 X 10(-7) M. The beta 2 identity of these receptors was determined by utilizing the relatively specific beta 1 and beta 2 antagonists practolol and ICI-118,551, respectively. Practolol failed to displace more than 30% of ICYP binding even at 100 microM, while ICI-118,551 displacement of ICYP yielded a linear Hofstee plot (r = 0.93) and a KD of 5.04 X 10(-9) M. These findings suggest that the secretory activity of Clara cell-like pulmonary adenomas is under beta-adrenergic control similar to that of normal bronchiolar Clara cells.
据报道，乙基硝基脲诱发的小鼠肺腺瘤主要起源于克拉拉细胞。研究了在向120日龄荷瘤小鼠腹腔注射后1小时，这些肿瘤细胞在体内对分泌激动剂异丙肾上腺素（10毫克/千克）和拮抗剂普萘洛尔（2.0毫克/千克）的反应。通过测量分泌颗粒的体积密度，采用超微结构形态计量学来定量肿瘤细胞的分泌反应。在完整动物中，异丙肾上腺素刺激克拉拉细胞腺瘤的分泌（体积密度降低40%，颗粒的表面积与体积比无变化），而普萘洛尔可阻止这种效应。此外，通过使用[125I]碘氰吲哚洛尔（ICYP）的放射性配体结合试验，在分离的肿瘤细胞上证实了β-肾上腺素能受体。对全细胞数据的Scatchard分析表明，最大受体结合能力为27飞摩尔/毫克蛋白质，解离常数（KD）为0.029纳摩尔。异丙肾上腺素对ICYP结合的置换产生的半数抑制浓度（IC50）为8×10^(-7)摩尔，计算得出的KD为3.36×10^(-7)摩尔。通过分别使用相对特异的β1和β2拮抗剂醋丁洛尔和ICI-118,551，确定了这些受体的β2身份。即使在100微摩尔时，醋丁洛尔也未能置换超过30%的ICYP结合，而ICI-118,551对ICYP的置换产生了线性Hofstee图（r = 0.93），KD为5.04×10^(-9)摩尔。这些发现表明，类克拉拉细胞肺腺瘤的分泌活性受β-肾上腺素能控制，类似于正常细支气管克拉拉细胞。
