The Absence of an Na+/Ca2+Exchanger (NCX) in Bullfrog Proximal Tubules and Cellular pH is More Influential Than Cellular Ca2+ on Proximal Na Transport.

IF 2.5 Q3 CELL BIOLOGY
Yutaka Matsumura
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引用次数: 0

Abstract

Background/aims: The functional significance of the Na+/Ca2+ exchanger (NCX) in basolateral membranes in the proximal tubule remains controversial. The key factor in crosstalk between the apical and basolateral sides is not known.

Methods: We investigated the basolateral membranes, using double-barreled Ca2+ or pH ion-selective microelectrodes. We used doubly perfused bullfrog kidneys in vivo, and switched the basolateral solution (renal portal vein) to experimental solutions.

Results: In the control, cellular pH (pHi) was 7.33 ± 0.032 (mean ± SE, n = 7) and in separate experiments, cellular Ca2+ activity (aCai) was 249.6 ± 35.54 nM (n = 28). Changing to respiratory acidosis, pHi was significantly acidified by 0.123 pH units on average and the change of aCai was +53.1 nM (n = 9 ns). In metabolic acidosis, pHi was reduced by 0.151 while aCai was reduced by 143.4. Using the 30 mM K+ solution, pHi was increased by 0.233 while aCai was reduced by 203.9, with depolarization. Both ionomycin and ouabain caused aCai to increase. In the 0.5 mM Na+ solution (replaced with BIDAC Cl), pHi was reduced by 0.177. No changes in aCai (+49.8 ns) were observed although we recorded depolarization of 15.2 mV. In the 0.5 mM Na+ solution, replaced with raffinose, no changes in aCai (-126.4 ns) were observed with depolarization (6.5 ns).

Conclusion: Our results suggest that thermodynamic calculations of cellular Na+ concentration led to the conclusion that either a Na+/HCO3- exchanger (NBC) or NCX could be present in the same basolateral membrane. H+ ions are the most plausible key factor in the crosstalk.

牛蛙近端小管和细胞pH中Na+/Ca2+交换剂(NCX)的缺失对近端Na转运的影响大于细胞Ca2+。
背景/目的:Na+/Ca2+交换器(NCX)在近端小管基底外侧膜中的功能意义仍然存在争议。在根尖侧和基底侧之间产生串扰的关键因素尚不清楚。方法:采用双管Ca2+或pH离子选择性微电极对基底外侧膜进行研究。我们在体内使用双灌注牛蛙肾脏,并将基底外侧溶液(肾门静脉)转换为实验溶液。结果:对照组细胞pH (pHi)为7.33±0.032 (mean±SE, n = 7),单独实验细胞Ca2+活性(aCai)为249.6±35.54 nM (n = 28)。pHi转变为呼吸性酸中毒,平均显著酸化0.123 pH单位,aCai变化+53.1 nM (n = 9 ns)。代谢性酸中毒时,pHi降低0.151,aCai降低143.4。在30 mM K+溶液中,pHi增加了0.233,aCai减少了203.9。离子霉素和沃卡因均引起aCai升高。在0.5 mM Na+溶液中(用BIDAC Cl代替),pHi降低了0.177。虽然我们记录了15.2 mV的去极化,但aCai (+49.8 ns)没有变化。在0.5 mM Na+溶液中,用棉子糖代替,去极化(6.5 ns)时aCai (-126.4 ns)没有变化。结论:我们的研究结果表明,细胞内Na+浓度的热力学计算得出结论,Na+/HCO3-交换剂(NBC)或NCX可能存在于同一基底外侧膜中。氢离子是串扰中最可信的关键因素。
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来源期刊
CiteScore
5.80
自引率
0.00%
发文量
86
审稿时长
1 months
期刊介绍: Cellular Physiology and Biochemistry is a multidisciplinary scientific forum dedicated to advancing the frontiers of basic cellular research. It addresses scientists from both the physiological and biochemical disciplines as well as related fields such as genetics, molecular biology, pathophysiology, pathobiochemistry and cellular toxicology & pharmacology. Original papers and reviews on the mechanisms of intracellular transmission, cellular metabolism, cell growth, differentiation and death, ion channels and carriers, and the maintenance, regulation and disturbances of cell volume are presented. Appearing monthly under peer review, Cellular Physiology and Biochemistry takes an active role in the concerted international effort to unravel the mechanisms of cellular function.
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