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Regulatory mechanism of proton transport across the tubular membranes of the bullfrog kidney



Regulatory mechanism of proton transport across the tubular membranes of the bullfrog kidney



Journal of Osaka Medical College 45(2): 265-279, 289



Double-barrelled liquid ion exchange pH microelectrodes were used to investigate the mechanism of renal tubular acid-base balance. The intracellular pH (pHi) and the peritubular membrane potential (EM) were determined in the bullfrog proximal tubule and sartorius muscle. Under normal control conditions, the measured pHi values were 7.32 and 7.21 in in vivo and in vitro perfused kidneys, and 6.85 in the sartorius muscle, with extracellular bicarbonate of 11.4 mM, 11 mmHg PCO2 and pH 7.6-7.7. Intracellular bicarbonate activities (aHCO3i) predicted from the measured pH and extracellular PCO2 were compared with those actually measured with bicarbonate selective microelectrodes. The predicted aHCO3i values were 4.7 mM and 5.2 mM in in vivo and in vitro perfused kidneys, and 1.7 mM in the sartorius muscle, while the measured aHCO3i were 5.9. mM, 5.3 mM and 1.6 mM, respectively. The agreement of aHOC3i obtained by both methods indicates that CO2 is completely in equilibrium between the two phases. When pHi was altered by changing external pH, PCO2, or HCO3-, a striking and consistent positive correlation was found between changes of EM and of pHi (r = 0.993), indicating that hyperpolarization was always associated with cell alkalinization. Peritubular ouabain (10-5 M) lowered the pHi with depolarization, whereas SITS (5 .times. 10-4 M) produced a rise in pHi without appreciable change in EM in the early phase, but later a hyperpolarization was produced in association with cell alkalinization. In these experiments, changes of Na+ chemical potential difference (.DELTA.ENa) and H+ chemical potential difference (.DELTA.EH) are energetically balanced with each other. The former is maintained by the basolateral Na+-K+ pump, whereas the latter is controlled by an Na+-H+ exchange mechanism in the luminal membrane and HCO3- exit through the basolateral membrane.

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Accession: 006292161

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