Immunolocalization of 15-kDa membrane proteins in the kidneys of normal and acidotic rats

Proteins with apparent molecular masses between 15 kDa and 17 kDa were enriched from rat renal brush-border membranes by preparative gel electrophoresis and used for immunization of rabbits. The serum of one of the rabbits reacted in Western blots of separated renal brush-border proteins with a single 15-kDa band. A comparably strong reaction is seen with a 15-kDa band of renal endosomal proteins. Basolateral membranes show a much weaker reaction. In light- and electron-microscopic studies the serum stains brush-border membranes and endosomes in rat proximal tubule cells, but not mitochondria and basolateral membranes. In cortical collecting ducts, principal cells are not stained with the antiserum. α-type (H+-secreting) intercalated cells bind the antibodies at apical tubulovesicles. The luminal membrane is scarcely labelled. Conversely, β-type (HCO−3 -secreting) intercalated cells exhibit antibody binding to their basolateral membrane. Thus, the antiserum detects 15-kDa proteins differently sorted in α -and β-intercalated cells. After induction of an acute (6 h) metabolic acidosis, the antibody-binding pattern changes only in intercalated cells, type α, and occurs at the markedly enlarged luminal plasma membrane. The amount of α-type intercalated cells with enlarged luminal membrane (“secreting cell”) increases at the expense of a cells with apical tubulovesicles (“resting cell”).Taken together, the antiserum detects 15-kDa proteins, the localization and adaptive changes to metabolic acidosis of which are similar to H+ -ATPases. The functional role of the 15-kDa proteins needs to be established in further studies