Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review
NBCn1 increases NH4+ reabsorption across thick ascending limbs, the capacity for urinary NH4+ excretion, and early recovery from metabolic acidosis. / Olsen, Jeppe Steen; Svendsen, Samuel Levi Svinth C; Berg, Peder et al.
In: Journal of the American Society of Nephrology, Vol. 32, No. 4, 04.2021, p. 852-865.Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review
}
TY - JOUR
T1 - NBCn1 increases NH4+ reabsorption across thick ascending limbs, the capacity for urinary NH4+ excretion, and early recovery from metabolic acidosis
AU - Olsen, Jeppe Steen
AU - Svendsen, Samuel Levi Svinth C
AU - Berg, Peder
AU - Dam, Vibeke Secher
AU - Sørensen, Mads Vaarby
AU - Matchkov, Vladimir
AU - Leipziger, Jens Georg
AU - Boedtkjer, Ebbe
PY - 2021/4
Y1 - 2021/4
N2 - BACKGROUND: The electroneutral Na +/HCO 3 - cotransporter NBCn1 (Slc4a7) is expressed in basolateral membranes of renal medullary thick ascending limbs (mTALs). However, direct evidence that NBCn1 contributes to acid-base handling in mTALs, urinary net acid excretion, and systemic acid-base homeostasis has been lacking. METHODS: Metabolic acidosis was induced in wild-type and NBCn1 knockout mice. Fluorescence-based intracellular pH recordings were performed and NH 4 + transport measured in isolated perfused mTALs. Quantitative RT-PCR and immunoblotting were used to evaluate NBCn1 expression. Tissue [NH 4 +] was measured in renal biopsies, NH 4 + excretion and titratable acid quantified in spot urine, and arterial blood gasses evaluated in normoventilated mice. RESULTS: Basolateral Na +/HCO 3 - cotransport activity was similar in isolated perfused mTALs from wild-type and NBCn1 knockout mice under control conditions. During metabolic acidosis, basolateral Na +/HCO 3 - cotransport activity increased four-fold in mTALs from wild-type mice, but remained unchanged in mTALs from NBCn1 knockout mice. Correspondingly, NBCn1 protein expression in wild-type mice increased ten-fold in the inner stripe of renal outer medulla during metabolic acidosis. During systemic acid loading, knockout of NBCn1 inhibited the net NH 4 + reabsorption across mTALs by approximately 60%, abolished the renal corticomedullary NH 4 + gradient, reduced the capacity for urinary NH 4 + excretion by approximately 50%, and delayed recovery of arterial blood pH and standard [HCO 3 -] from their initial decline. CONCLUSIONS: During metabolic acidosis, NBCn1 is required for the upregulated basolateral HCO 3 - uptake and transepithelial NH 4 + reabsorption in mTALs, renal medullary NH 4 + accumulation, urinary NH 4 + excretion, and early recovery of arterial blood pH and standard [HCO 3 -]. These findings support that NBCn1 facilitates urinary net acid excretion by neutralizing intracellular H + released during NH 4 + reabsorption across mTALs.
AB - BACKGROUND: The electroneutral Na +/HCO 3 - cotransporter NBCn1 (Slc4a7) is expressed in basolateral membranes of renal medullary thick ascending limbs (mTALs). However, direct evidence that NBCn1 contributes to acid-base handling in mTALs, urinary net acid excretion, and systemic acid-base homeostasis has been lacking. METHODS: Metabolic acidosis was induced in wild-type and NBCn1 knockout mice. Fluorescence-based intracellular pH recordings were performed and NH 4 + transport measured in isolated perfused mTALs. Quantitative RT-PCR and immunoblotting were used to evaluate NBCn1 expression. Tissue [NH 4 +] was measured in renal biopsies, NH 4 + excretion and titratable acid quantified in spot urine, and arterial blood gasses evaluated in normoventilated mice. RESULTS: Basolateral Na +/HCO 3 - cotransport activity was similar in isolated perfused mTALs from wild-type and NBCn1 knockout mice under control conditions. During metabolic acidosis, basolateral Na +/HCO 3 - cotransport activity increased four-fold in mTALs from wild-type mice, but remained unchanged in mTALs from NBCn1 knockout mice. Correspondingly, NBCn1 protein expression in wild-type mice increased ten-fold in the inner stripe of renal outer medulla during metabolic acidosis. During systemic acid loading, knockout of NBCn1 inhibited the net NH 4 + reabsorption across mTALs by approximately 60%, abolished the renal corticomedullary NH 4 + gradient, reduced the capacity for urinary NH 4 + excretion by approximately 50%, and delayed recovery of arterial blood pH and standard [HCO 3 -] from their initial decline. CONCLUSIONS: During metabolic acidosis, NBCn1 is required for the upregulated basolateral HCO 3 - uptake and transepithelial NH 4 + reabsorption in mTALs, renal medullary NH 4 + accumulation, urinary NH 4 + excretion, and early recovery of arterial blood pH and standard [HCO 3 -]. These findings support that NBCn1 facilitates urinary net acid excretion by neutralizing intracellular H + released during NH 4 + reabsorption across mTALs.
KW - AMMONIUM
KW - CELLS
KW - COTRANSPORTER NBCN1
KW - INTRACELLULAR PH
KW - LOCALIZATION
KW - NA+
KW - PERFUSION
KW - S0859
KW - SLC4A7
KW - TRANSPORT
KW - acidosis
KW - cell & transport physiology
KW - intracellular pH
KW - ion transport
U2 - 10.1681/ASN.2019060613
DO - 10.1681/ASN.2019060613
M3 - Journal article
C2 - 33414245
VL - 32
SP - 852
EP - 865
JO - Journal of the American Society of Nephrology
JF - Journal of the American Society of Nephrology
SN - 1046-6673
IS - 4
ER -