| Abstract: | In previousstudies, our laboratory has utilized a cell line derived from the ratinner medullary collecting duct (IMCD) as a model system for mammalianrenal epithelial cell acid secretion. We have provided evidence, from aphysiological perspective, that acute cellular acidification stimulatesapical exocytosis and elicits a rapid increase in proton secretion thatis mediated by an H+-ATPase. Thepurpose of these experiments was to examine the effect of acutecellular acidification on the distribution of the vacuolar H+-ATPase in IMCD cells in vitro.We utilized the 31-kDa subunit of theH+-ATPase as a marker of thecomplete enzyme. The distribution of this subunit of theH+-ATPase was evaluated byimmunohistochemical techniques (confocal and electron microscopy), andwe found that there is a redistribution of these pumps from vesicles tothe apical membrane. Immunoblot evaluation of isolated apical membranerevealed a 237 ± 34% (P < 0.05, n = 9) increase in the 31-kDa subunitpresent in the membrane fraction 20 min after the induction of cellularacidification. Thus our results demonstrate the presence of this pumpsubunit in the IMCD cell line in vitro and that cell acidificationregulates the shuttling of cytosolic vesicles containing the 31-kDasubunit into the apical membrane. |
