Reshkin S J, Forgo J, Murer H
Department of Physiology, University of Zürich, Switzerland.
J Membr Biol. 1991 Dec;124(3):227-37. doi: 10.1007/BF01994356.
The cellular distribution (apical vs. basolateral) of parathyroid hormone (PTH) signal transduction systems in opossum kidney (OK) cells was evaluated by measuring the action of PTH on apically located transport processes (Na/Pi cotransport and Na/H exchange) and on the generation of intracellular messengers (cAMP and IP3). PTH application led to immediate inhibition of Na/H-exchange without a difference in dose/response relationships between apical and basolateral cell-surface hormone addition (half-maximal inhibition at approximately 5 x 10(-12) M). PTH required 2-3 hr for maximal inhibition of Na/Pi cotransport with a half-maximal inhibition occurring at approximately 5 x 10(-10) M PTH for basolateral application and approximately 5 x 10(-12) M for apical application. PTH addition to either side of the monolayer produced a dose-dependent production of both cAMP and IP3. Half-maximal activation of IP3 was at about 7 x 10(-12) M PTH and displayed no differences between apical and basolateral hormone addition, while cAMP was produced with a half maximal concentration of 7 x 10(-9) M for apical PTH application and 10(-9) M for basolateral administration. The PTH analog [nle8.18,tyr34]PTH(3-34), (nlePTH), produced partial inhibition of Na/Pi cotransport (agonism) with no difference between apical and basolateral application. When applied as a PTH antagonist, nlePTH displayed dose-dependent antagonism of PTH inhibition of Na/Pi cotransport on the apical surface, failing to have an effect on the basolateral surface. Independent of addition to the apical or basolateral cell surface, nlePTH had only weak stimulatory effect on production of cAMP, whereas high levels of IP3 could be measured after addition of this PTH analog to either cell surface. Also an antagonistic action of nlePTH on PTH-dependent generation of the internal messengers, cAMP and IP3, was observed; at the apical and basolateral cell surface nelPTH reduced PTH-dependent generation of cAMP, while PTH-dependent generation of IP3 was only reduced by nlePTH at the apical surface. Pertussis toxin (PT) preincubation produced an attenuation of both PTH-dependent inhibition of Na/Pi cotransport and 1P3 generation while producing an enhancement of PTH-dependent cAMP generation; these effects displayed no cell surface polarity, suggesting that PTH action through either adenylate cyclase or phospholipase C was transduced through similar sets of G-proteins at each cell surface.
通过检测甲状旁腺激素（PTH）对位于顶端的转运过程（钠/磷酸盐共转运和钠/氢交换）以及细胞内信使（环磷酸腺苷（cAMP）和肌醇三磷酸（IP3））生成的作用，评估了负鼠肾（OK）细胞中PTH信号转导系统的细胞分布（顶端与基底外侧）。施加PTH可立即抑制钠/氢交换，顶端和基底外侧细胞表面添加激素之间的剂量/反应关系无差异（在约5×10⁻¹² M时达到半数最大抑制）。PTH需要2 - 3小时才能最大程度抑制钠/磷酸盐共转运，基底外侧施加时在约5×10⁻¹⁰ M PTH时达到半数最大抑制，顶端施加时约为5×10⁻¹² M。向单层细胞的任一侧添加PTH都会产生剂量依赖性的cAMP和IP3生成。IP3的半数最大激活浓度约为7×10⁻¹² M PTH，顶端和基底外侧添加激素之间无差异，而顶端施加PTH时cAMP的半数最大生成浓度为7×10⁻⁹ M，基底外侧施加时为10⁻⁹ M。PTH类似物[nle8.18,tyr34]PTH(3 - 34)（nlePTH）对钠/磷酸盐共转运产生部分抑制（激动作用），顶端和基底外侧施加之间无差异。当作为PTH拮抗剂应用时，nlePTH对顶端表面PTH抑制钠/磷酸盐共转运表现出剂量依赖性拮抗作用，对基底外侧表面无影响。无论添加到顶端还是基底外侧细胞表面，nlePTH对cAMP生成只有微弱的刺激作用，而将这种PTH类似物添加到任一细胞表面后均可检测到高水平的IP3。还观察到nlePTH对PTH依赖性细胞内信使cAMP和IP3生成的拮抗作用；在顶端和基底外侧细胞表面，nlePTH降低了PTH依赖性cAMP的生成，而PTH依赖性IP3的生成仅在顶端表面被nlePTH降低。百日咳毒素（PT）预孵育使PTH依赖性钠/磷酸盐共转运抑制和IP3生成均减弱，同时使PTH依赖性cAMP生成增强；这些效应无细胞表面极性，表明PTH通过腺苷酸环化酶或磷脂酶C的作用是通过每个细胞表面相似的一组G蛋白转导的。
