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.
{"title":"The Absence of an Na<sup>+</sup>/Ca<sup>2+</sup>Exchanger (NCX) in Bullfrog Proximal Tubules and Cellular pH is More Influential Than Cellular Ca<sup>2+</sup> on Proximal Na Transport.","authors":"Yutaka Matsumura","doi":"10.33594/000000641","DOIUrl":null,"url":null,"abstract":"<p><strong>Background/aims: </strong>The functional significance of the Na<sup>+</sup>/Ca<sup>2+</sup> 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.</p><p><strong>Methods: </strong>We investigated the basolateral membranes, using double-barreled Ca<sup>2+</sup> or pH ion-selective microelectrodes. We used doubly perfused bullfrog kidneys in vivo, and switched the basolateral solution (renal portal vein) to experimental solutions.</p><p><strong>Results: </strong>In the control, cellular pH (pH<sub>i</sub>) was 7.33 ± 0.032 (mean ± SE, n = 7) and in separate experiments, cellular Ca<sup>2+</sup> activity (aCa<sub>i</sub>) was 249.6 ± 35.54 nM (n = 28). Changing to respiratory acidosis, pH<sub>i</sub> was significantly acidified by 0.123 pH units on average and the change of aCa<sub>i</sub> was +53.1 nM (n = 9 ns). In metabolic acidosis, pH<sub>i</sub> was reduced by 0.151 while aCa<sub>i</sub> was reduced by 143.4. Using the 30 mM K<sup>+</sup> solution, pH<sub>i</sub> was increased by 0.233 while aCa<sub>i</sub> was reduced by 203.9, with depolarization. Both ionomycin and ouabain caused aCa<sub>i</sub> to increase. In the 0.5 mM Na<sup>+</sup> solution (replaced with BIDAC Cl), pH<sub>i</sub> was reduced by 0.177. No changes in aCa<sub>i</sub> (+49.8 ns) were observed although we recorded depolarization of 15.2 mV. In the 0.5 mM Na<sup>+</sup> solution, replaced with raffinose, no changes in aCa<sub>i</sub> (-126.4 ns) were observed with depolarization (6.5 ns).</p><p><strong>Conclusion: </strong>Our results suggest that thermodynamic calculations of cellular Na<sup>+</sup> concentration led to the conclusion that either a Na<sup>+</sup>/HCO<sub>3</sub><sup>-</sup> exchanger (NBC) or NCX could be present in the same basolateral membrane. H<sup>+</sup> ions are the most plausible key factor in the crosstalk.</p>","PeriodicalId":9845,"journal":{"name":"Cellular Physiology and Biochemistry","volume":"57 4","pages":"238-263"},"PeriodicalIF":2.5000,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Cellular Physiology and Biochemistry","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.33594/000000641","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"CELL BIOLOGY","Score":null,"Total":0}
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.
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.