Sm. Ginns et al., IMMUNOLOCALIZATION OF THE SECRETORY ISOFORM OF NA-K-CL COTRANSPORTER IN RAT RENAL INTERCALATED CELLS, Journal of the American Society of Nephrology, 7(12), 1996, pp. 2533-2542
Two bumetanide-sensitive ion cotransporters that carry Na+, K+, and Cl
- in a coupled fashion have been identified. One type, the ''absorptiv
e'' isoform, carries these ions across the apical plasma membrane of;t
he thick ascending limb of Henle's loop. Another isoform, the ''secret
ory'' cotransporter, has been identified in a number of epithelial tis
sues by physiological means, but its sites of expression in the kidney
have not been fully characterized, Complementary DNA believed to code
for the secretary isoform (called ''BSC2'' or ''NKCC1'') have recentl
y been cloned, This study used a specific affinity-purified antipeptid
e antibody to this protein for immunolocalization in the rat kidney. I
mmunoblot studies using this antibody show abundant immunoreactivity a
gainst bands of 140-190 and 120 kd in the parotid gland, colon, and st
omach, sites where the secretory form of the cotransporter has been id
entified by physiological techniques. This distribution supports the h
ypothesis that this isoform represents the secretory form of the cotra
nsporter. Studies in the kidney revealed that the same bands are assoc
iated with membrane fractions chiefly in the outer medulla, Immunoloca
lizations show that immunoreactivity is selectively and intensely loca
lized to the basolateral plasma membrane of a subfraction of outer med
ullary collecting duct cells. An independently produced monoclonal ant
ibody (T4) specific for Na-K-Cl cotransporter displays the same locali
zation. Dual localizations of cotransporter antibody with respect to a
ntibody specific for principal cells (aquaporin-2) and intercalated ce
lls (band 3 and H+-ATPase) show that cotransporter immunoreactivity is
localized to alpha-intercalated cells of the outer medullary collecti
ng duct in the rat. This distinctive localization suggests that the se
cretory form of the cotransporter may play a role in renal NH4+ and/or
acid secretion by this cell type.