Picotto G, Massheimer V, Boland R
Departamento de Biología, Bioquímica, y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina.
Am J Physiol. 1997 Oct;273(4):C1349-53. doi: 10.1152/ajpcell.1997.273.4.C1349.
Direct effects of parathyroid hormone (PTH) on calcium uptake by isolated rat duodenal cell preparations enriched in enterocytes were investigated. PTH significantly stimulated enterocyte 45Ca2+ influx in a time-dependent (1-10 min) manner and at all doses tested (2 x 10(-13) to 10(-7) M). The Ca2+ channel antagonists verapamil (10 microM) and nitrendipine (1 microM) completely blocked the stimulation of Ca2+ influx by the hormone (10(-8) M). PTH markedly increased cAMP levels in rat duodenal cells (88, 167, and 67%, after 1, 2, and 3 min, respectively). In agreement with these observations, forskolin (adenylate cyclase activator), dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), and Sp-cAMPS (cAMP analogs) mimicked, whereas Rp-cAMPS (cAMP antagonist) suppressed PTH and DBcAMP activation of enterocyte calcium uptake. Furthermore, the effects of DBcAMP were abolished by nitrendipine. These results show direct rapid effects of PTH on duodenal cells' Ca2+ influx, which involve the activation of a dihydropyridine-sensitive Ca2+ influx pathway and the cAMP second messenger system.
研究了甲状旁腺激素（PTH）对富含肠细胞的离体大鼠十二指肠细胞制剂摄取钙的直接作用。PTH以时间依赖性方式（1 - 10分钟）且在所有测试剂量（2×10⁻¹³至10⁻⁷ M）下均显著刺激肠细胞45Ca²⁺内流。Ca²⁺通道拮抗剂维拉帕米（10 μM）和尼群地平（1 μM）完全阻断了激素（10⁻⁸ M）对Ca²⁺内流的刺激。PTH显著提高了大鼠十二指肠细胞中的cAMP水平（分别在1、2和3分钟后提高了88%、167%和67%）。与这些观察结果一致，福司可林（腺苷酸环化酶激活剂）、二丁酰腺苷3',5'-环磷酸（DBcAMP）和Sp-cAMPS（cAMP类似物）模拟了PTH的作用，而Rp-cAMPS（cAMP拮抗剂）则抑制了PTH和DBcAMP对肠细胞钙摄取的激活。此外，尼群地平消除了DBcAMP的作用。这些结果表明PTH对十二指肠细胞的Ca²⁺内流有直接快速作用，这涉及激活对二氢吡啶敏感的Ca²⁺内流途径和cAMP第二信使系统。
