Protein Trafficking

Delivering an Acid Response

Science's STKE  09 Dec 2003:
Vol. 2003, Issue 212, pp. tw474-TW474
DOI: 10.1126/stke.2122003TW474

Pastor-Soler et al. used rat epididymus as a model system in which to investigate the role of soluble adenylyl cyclase (sAC), a form of adenylyl cyclase that is activated by bicarbonate, in the ability of epithelial cells to sense and respond to changes in pH. Clear cells, a subpopulation of epididymal epithelial cells, secrete protons into the epididymal lumen to maintain an acid pH. The rate of proton secretion depends on recycling of vacuolar H+ATPase (V-ATPase) between intracellular vesicles and the apical plasma membrane; however, the mechanisms governing this response remain unclear. Pastor-Soler et al. used reverse transcription polymerase chain reaction on rat epididymal epithelial cells harvested by laser capture microdissection combined with Western and immunofluorescence analysis of rat epididymus to confirm the presence of sAC in clear cells. The authors used confocal microscopy in combination with immunofluorescence and electron microscopy in combination with immunogold to monitor V-ATPase localization. In epididymus perfused with acidic saline, V-ATPase recycled between endosomes and the apical membrane, whereas alkaline pH promoted accumulation of V-ATPase in apical microvilli as did both a permeant analog of adenosine 3′,5′-monophosphate (cAMP) and bicarbonate. Pharmacologic inhibition of carbonic anhydrase indicated that bicarbonate production was essential for the response to alkaline pH but not to cAMP. Inhibition of sAC confirmed that this enzyme mediated the response to pH and to bicarbonate. This research establishes sAC as a critical mediator of a cellular response to changes in ambient pH, which may represent a widespread signaling pathway.

N. Pastor-Soler, V. Beaulieu, T. N. Litvin, N. Da Silva, Y. Chen, D. Brown, J. Buck, L. R. Levin, S. Breton, Bicarbonate-regulated adenylyl cyclase (sAC) is a sensor that regulates pH-dependent V-ATPase recycling. J. Biol. Chem. 278, 49523-49529 (2003). [Abstract] [Full Text]