The influence of extracellular calcium sensing receptor (CaR) on H+‐ATPases activity in mice kidney

Abstract

With the exception of the glomerulus, the CaR is highly expressed in all renal tubular segments. The aim of this project was to investigate the interaction between CaR and proton extrusion by the vacuolar H+‐ATPase (H+‐ATPase) and gastric‐like isoform of the H+/K+‐ATPase in mice nephron. Biochemical activity of H+‐ATPases was performed using a partially purified membrane fraction of mice cortex and outer medullar region. The inorganic phosphate (Pi) released in the reaction was quantified by a colorimetric reaction and enzyme activity was expressed in nmol of Pi.min−1.mg−1 of protein. This preparation present a bafilomycin (10−7M) sensitive activity (H+ ATPase), and a Schering 28080 (10−5M) sensitive activity (gastric H+/K+ ATPase), both in cortex and outer medullar region. The H+‐ATPase activity from cortical and outer medullary region was significantly stimulated by increasing the Ca2+o, in a dose‐dependent pattern. In the same way, gastric H+/K+‐ATPase activity was sensitive to changes in Ca2+o levels. A significant increase of H+‐ATPase activity was also observed when the CaR was stimulated with agonists such as 300μM Gd3+ and 200μM neomycin, both in cortex: 9,2 ± 1,2 basal vs 16,5 ± 2,9 with Gd3+, and 12,5 ± 2,2 nmol with neomycin, n=10; and outer medulla: 12,3 ± 1,4 basal vs 28,5 ± 3,3 with Gd3+, and 17,9 ± 2,4 with neomycin (n=10). The cortical and outer medullar gastric H+/K+‐ATPase activity was also stimulated by Gd3+ and neomycin. Finally, cortical H+‐ATPase activity was significantly stimulated by 10−9M angiotensin II (16,6 ± 2,1 basal vs 22,0 ± 2,8 with angiotensin, n=7), and the stimulation of CaR in the presence of angiotensin enhanced significantly these effect: 27,7±2,1 with angiotensin plus Gd3+, n=7, suggesting an interaction in the intracellular signaling pathways involved. These data allow us to conclude that CaR enhance proton secretion in both cortical and outer medulla region of mice kidney, by activation of H+‐ATPase and gastric H+/K+‐ATPase.