NDT Advance Access originally published online on June 24, 2006
Nephrology Dialysis Transplantation 2006 21(10):2762-2767; doi:10.1093/ndt/gfl335
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Defect in parathyroid-hormone-induced luminal calcium absorption in connecting tubules of Klotho mice
1Division of Clinical Pharmacology, Department of Pharmacology, Jichi Medical University, Tochigi 2Second Department of Internal Medicine, Gumma University School of Medicine, Gumma and 3Department of Cardiovascular Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
Correspondence and offprint requests to: Shuichi Tsuruoka, MD, Division of Clinical Pharmacology, Department of Pharmacology, Jichi Medical University, 3311 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan. Email: tsuru{at}jichi.ac.jp
Background. Homozygous Klotho mutant mice (KL–/– mice) exhibit multiple phenotypes resembling human ageing. Increases in the ratio of urinary calcium to urinary creatinine (uCa/uCr) and in serum Ca concentration and decreases in urinary Cr excretion and serum parathyroid hormone (PTH) concentration were reported; however, precise information about renal Ca handling was not reported in these animals.
Methods. We evaluated the PTH-induced increase in intracellular Ca2+ concentration ([Ca2+]i) in cells of isolated perfused connecting tubules (CNTs) of KL–/– mice. We also determined fractional excretion of Ca from the urine and serum samples of the same animals (n = 7), and compared them with KL+/+ mice and hemi-nephrectomized KL–+/+ mice (n = 10 in each) as controls.
Results. FECa was significantly higher in KL–/– mice than in controls (0.67 ± 0.13 vs 0.20 ± 0.04%). The PTH (10 nM)-induced increase in [Ca2+]i was diminished in KL–/– mice (58 ± 5 vs 231 ± 15 nM). Addition of 10 nM of 8-(4-chlorophenylthio)-cyclic adenosine 3',5'-monophosphate had a similar effect. The PTH-induced increase had completely disappeared by the removal of Ca from lumen and bath in both groups of animals. Removal of sodium (Na) from the solution increased [Ca2+]i to a similar extent in both groups.
Conclusion. We conclude that renal Ca excretion estimated by determining FECa was defective in the KL–/– mice. Impairment of Ca absorption from the lumen by stimulation of PTH in CNTs is one of the mechanisms of this defect. Activity of the basolateral Na/Ca exchanger was preserved in this strain. Therefore, the pathway downstream after generation of second messengers following stimulation of PTH (such as the sorting of transporters of Ca absorption) might be impaired by disruption of the Klotho gene.
Keywords: calcium absorption; connecting tubule; Klotho; PTH
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