Abstract
To examine the mechanisms of H+ transport in the mid-inner medullary collecting duct of hamsters, we measured the intracellular pH (pHi) in the in vitro perfused tubules by microscopic fluorometry using 2′,7′-bis(carboxyethyl)-carboxyfluorescein (BCECF) as a fluorescent probe. In the basal condition, pHi was 6.74±0.04 (n=45) in HCO −3 -free modified Ringer solution. Either elimination of Na+ from the bath or addition of amiloride (1 mM) to the bath produced a reversible fall in pHi After acid loading with 25 mM NH4Cl, pHi spontaneously recovered with an initial recovery rate of 0.096±0.012 (n=23) pH unit/min. In the absence of ambient Na+, after removal of NH +4 , the pHi remained low (5.95±0.10, n=8) and showed no signs of recovery. Subsequent restoration of Na+ only in the lumen had no effect on pHi. However, when Na+ in the bath was returned to the control level, pHi recovered completely. Amiloride (1 mM) in the bath completely inhibited the Na+-dependent pHi recovery. Furthermore, elimination of Na+ from the bath, but not from the lumen, decreased pHi from 6.97±0.07 to 6.44±0.05 (n=12) in the HCO −3 /Ringer solution or 6.70±0.03 to 6.02±0.05 (n=8) in the HCO −3 free solution. pHi spontaneously returned to 6.76±0.08 with a recovery rate of 0.017±0.5 pH unit/min in the presence of CO2/HCO −3 , whereas it did not recover in the absence of CO2/HCO −3 . Although elimination of ambient Na+ depolarized the basolateral membrane voltage (V B) from −78±1.2 to −72 ±0.6 mV (n=5, P<0.01), the level of V B was not sufficient to explain the pHi recovery solely by HCO −3 entry driven by the voltage. These results indicate that (a) pHi of the inner medullary collecting duct is regulated mainly by a Na+/H+ exchanger in the basolateral membranes, (b) no apparent Na+-dependent H+ transport system exists in the luminal membranes and (c) Na+-independent H+ transport may also operate in the presence of CO2/HCO −3
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Preliminary data were reported at the Conference on Bicarbonate, Chloride, and Proton Transport Systems, New York, USA, in January 1989
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Matsushima, Y., Yoshitomi, K., Koseki, C. et al. Mechanisms of intracellular pH regulation in the hamster inner medullary collecting duct perfused in vitro. Pflügers Arch 416, 715–721 (1990). https://doi.org/10.1007/BF00370620
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DOI: https://doi.org/10.1007/BF00370620