Bellorin-Font E, Starosta R, Milanes C L, Lopez C, Pernalete N, Weisinger J, Paz-Martinez V
Centro Nacional de Dialisis y Trasplante, Hospital Universitario de Caracas, Venezuela.
Am J Physiol. 1990 Jun;258(6 Pt 2):F1640-9. doi: 10.1152/ajprenal.1990.258.6.F1640.
These studies examine the regulation of adenylate cyclase in renal cortical membranes from phosphate-deprived and phosphate-deprived acidotic dogs. Enzyme stimulation by parathyroid hormone (PTH) was decreased in phosphate deprivation [Vmax 1,578 +/- 169 vs. 2,581 +/- 219 pmol adenosine 3',5'-cyclic monophosphate (cAMP).mg protein-1 x 30 min-1 in controls, P less than 0.01]. Metabolic acidosis further decreased PTH-stimulated activity. Membranes from phosphate-deprived dogs showed a decrease in Gs alpha-content by cholera toxin-dependent ADP-ribosylation (174 +/- 18 arbitrary units vs. 266.4 +/- 13.6 in controls, P less than 0.01). Metabolic acidosis further decreased Gs alpha-content, P less than 0.01. Gi content by pertussis-dependent ADP-ribosylation was also lower in phosphate-deprived and phosphate-deprived acidotic animals. Gs function was examined by its property to protect the catalytic unit from inactivation by N-ethylmaleimide when preincubated with GTP gamma S. In controls, protection of inactivation was 80% of the maximal activity, whereas in phosphate deprivation protection was less than 50%. In conclusion, metabolic acidosis enhances adenylate cyclase resistance to PTH in phosphate deprivation. These alterations are associated with a decrease in the content and function of Gs alpha, suggesting a role of Gs in the renal adaptation to phosphate depletion and acidosis.
这些研究检测了来自低磷和低磷酸中毒犬肾皮质膜中腺苷酸环化酶的调节情况。甲状旁腺激素（PTH）对酶的刺激作用在低磷状态下降低[最大反应速度（Vmax）：对照组为2,581±219 pmol腺苷3',5'-环磷酸（cAMP）·mg蛋白⁻¹×30 min⁻¹，低磷组为1,578±169，P<0.01]。代谢性酸中毒进一步降低了PTH刺激的活性。通过霍乱毒素依赖性ADP核糖基化检测发现，低磷犬的肾皮质膜中Gsα含量降低（174±18任意单位，对照组为266.4±13.6，P<0.01）。代谢性酸中毒进一步降低了Gsα含量，P<0.01。通过百日咳毒素依赖性ADP核糖基化检测发现，低磷和低磷酸中毒动物的Gi含量也较低。通过在与GTPγS预孵育时保护催化亚基不被N-乙基马来酰亚胺灭活的特性来检测Gs的功能。在对照组中，灭活保护作用为最大活性的80%，而在低磷状态下保护作用小于50%。总之，代谢性酸中毒增强了低磷状态下腺苷酸环化酶对PTH的抵抗性。这些改变与Gsα含量和功能的降低有关，提示Gs在肾脏适应磷缺乏和酸中毒中起作用。
