Intracellular pH regulation by the plasma membrane V-ATPase in Malpighian tubules of Drosophila larvae

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 164; no. 3; pp. 238 - 246
• Main Authors: Bertram, G, Wessing, A
• Format: Journal Article
• Language: English
• Published: Germany 1994
• Subjects: Acids - pharmacology; Adenosine Triphosphatases - physiology; adenosinetriphosphatase; Ammonium Chloride - pharmacology; Animals; Antiporters - metabolism; Buffers; Cell Membrane - enzymology; Drosophila; Drosophila - metabolism; Homeostasis; Hydrogen - metabolism; Hydrogen-Ion Concentration; Intracellular Membranes - metabolism; Malpighian tubules; Malpighian Tubules - metabolism; plasma membrane; Potassium-Hydrogen Antiporters; regulation; Vacuoles - enzymology
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/BF00354085

The functional significance of the apical vacuolar-type proton pump (V-ATPase) in Drosophila Malpighian tubules was studied by measuring the intracellular pH (pH(i)) and luminal pH (pH(lu)) with double-barrelled pH-microelectrodes in proximal segments of the larval anterior tubule immersed in nominally bicarbonate-free solutions (pH(o) 6.9). In proximal segments both pH(i) (7.43 +/- 0.20) and pH(lu) (7.10 +/- 0.24)) were significantly lower than in distal segments (pH(i) 7.70 +/- 0.29, pH(lu) 8.09 +/- 0.15). Steady-state pH(i) of proximal segments was much less sensitive to changes in pH(o) than pH of the luminal fluid (delta pH(lu)/delta pH(o) was 0.49 while delta pH(i)/delta pH(o) was 0.18; pH(o) 6.50-7.20). Re-alkalinization from an NH4Cl-induced intracellular acid load (initial pH(i) recovery rate 0.55 +/- 0.34 pH/min(-1)) was nearly totally inhibited by 1 mmol/l(-1) KCN (96% inhibition) and to a large degree (79%) by 1 micromole.l(-1) bafilomycin A(1). In contrast, both vanadate (1 mmol.l(-1)) and amiloride (1 mmol.l(-1)) inhibited pH(i) recovery by 38% and 33%, respectively. Unlike amiloride, removal of Na+ from the bathing saline had no effect on pH(i) recovery, indicating that a Na+/H+ exchange is not significantly involved in pH(i) regulation. Instead pH(i) regulation apparently depended largely on the availability of ATP and on the activity of the bafilomycin-sensitive proton pump.