In vivo microelectrode assessment of NBCe2 activity in the distal nephron during an acid load (1122.2)

The electrogenic Na bicarbonate co‐transporter (NBCe2) reabsorbs one Na and two or three bicarbonates in the distal nephron but its electrogenic function has not been demonstrated in‐vivo . Micropuncture was used to determine the transepithelial potential (Vte) in the distal convoluted tubule 2 (DCT2) of wild type mice (WT) and mice with a knock‐out of NBCe2 (NBCe2‐/‐). The DCT2 is the segment where expression of ENaC‐mediated Na reabsorption and ROMK‐mediated K secretion begins. Fine tip microelectrodes were placed in the lumen of the DCT2. A ground reference electrode was placed in the surface saline solution near the luminal microelectrode. Each group: n 蠅 3. We validated the microelectrode measurements by determining the effects on Vte of proximal tubule in control (‐5.6 ± 0.3 mV) and after giving 2% IP phloridzin (Vte = ‐0.2 ± 0.2 mV), an inhibitor of Na‐glucose cotransport. The Vte of the DCT2 was ‐11.0 ± 0.6 mV in WT control diet mice. When treated with acidic (280 mM NH 4 Cl) drinking water, the Vte of WT decreased to 0.4 ± 1.1 mV, a value significantly greater than WT, consistent with H+ secretion and/or bicarbonate reabsorption in this segment. When treated with acid water, the Vte of NBCe2‐/‐ was ‐3.4 ± 0.3 mV, a value significantly less than that of WT on acid water. We conclude that the NBCe2 is located in the DCT2 where it contributes to a more positive luminal potential when mice consume an acid load. Grant Funding Source : NIDDK