Intracellular pH in diluting segment of frog kidney

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Abstract
Chronic exposure to high potassium (K+ adaptation) stimulates H+ net secretion in the diluting segment of the frog kidney. In order to investigate the cellular mechanism of the H+ secretory process intracellular pH (pHi) measurements were performed in cells of the diluting segment of the isolated doubly-perfused kidney of K+ adaptedRana esculenta. pHi changes were monitored by pH-sensitive microelectrodes while the tubule lumen was rapidly perfused with various solutions. With control solutions (extracellular pH=7.80) pHi averaged 7.60±0.05. Luminal application of furosemide (5 · 10−5 mol/l) or reduction of luminal Cl− (from 104 mmol/l to 9 mmol/l) hyperpolarized the cell membrane potentials but pHi was not altered. Reduction of luminal Na+ (from 98 mmol/l to 3 mmol/l) depolarized the cell membrane potentials but pHi remained constant. Complete removal of luminal Na+, however, led to a significant decrease of pHi from 7.61±0.08 to 7.18±0.08. Luminal application of amiloride (1 · 10−3 mol/l) also decreased pHi significantly (ΔpHi=0.15±0.02). The results indicate that an amiloride-sensitive H+ extrusion mechanism exists in the luminal cell membrane of the K+ adapted frog diluting segment. The data are consistent with Na+/H+ exchange which maintains a constant pHi even at extreme experimental conditions.

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