Developmental analyses of Ca transporters and Ca sensing receptors in the kidneys

尿液浓缩机制是一种仅在鸟类和哺乳动物中进化出来的生物学机制。我们最近的研究表明，尿浓缩机制的发育变化不是量变，而是质变。新生儿发育的核心组成部分是尿液浓缩系统从单一的氯化钠积累系统过渡到复杂的尿素-氯化钠积累系统。在本研究项目中，我们分析了新生儿钙稳态与尿浓缩机制发展的关系。我们特别关注分布在每个肾小管段的钙敏感受体的发展。为分析钙敏感受体（CSR）在调节肾小管功能中的作用，体外微灌注Henle’s loop外髓增厚升肢。在新生小鼠中，CSR激动剂新霉素略微增加细胞内Ca活性，但不改变基底外侧细胞内pH。基底外侧溶液中的新霉素使成体金属tal细胞酸化，而对细胞内钙活性没有影响。氨酰脲或阴离子转运抑制剂DIDS不抑制新霉素对细胞的酸化作用。新生儿肾片的mTAL未显示CSR免疫反应性。这些结果强烈表明，CSR在新生儿tal中没有发展。CSR对细胞酸化的确切机制有待于进一步的研究。

Urine concentrating mechanism is a biological mechanism that has evolved only in birds and mammals. Our recent studies have revealed that developmental changes of the urine concentrating mechanism are not the quantitative changes but the qualitative changes. The core component of the neonatal development is the transition of the urine concentrating system from the sole NaCl-aocumulating system to the complex Urea-NaCl accumulating system.In the present research project, we analyzed the relationship between neonatal calcium homeostasis and the development of urine-concentrating mechanism. We especially focused on the development of calciuum-sensing receptors distributed to each renal tubule segments.To analyze the contribution of calcium-sensing receptor (CSR) in the regulation of tubular function, the outer medullary thick ascending limbs of Henle's loop (mTAL) were microperfused in vitro. In the neonatal mice, neomycin the CSR agonist slightly increased intracellular Ca activity without changing intracellular pH from the basolateral side. Neomycin in the basolateral solution acidified the cells of the adult mTAL, whereas it had no effect on intracellular Ca activities. Acidification of the cells by neomycin was not inhibited by amiloride or the anion transport inhibitor DIDS. CSR immunoreactivity was not demonstrated in the mTAL of the neonatal kidney slices.These results strongly suggest that the CSR is not developed in the neonatal mTAL. The precise mechanism of acidification of cells by CSR is to be analyzed more in the future studies.