Macula densa Na⁺/H⁺exchange activities mediated by apical NHE2 and basolateral NHE4 isoforms

Abstract

Functional and immunohistochemical studies were performed to localize and identify Na(+)/H(+) exchanger (NHE) isoforms in macula densa cells. By using the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney, intracellular pH (pH(i)) was measured with fluorescence microscopy by using 2',7'-bis-(2-carboxyethyl)-5-(and -6) carboxyfluorescein. NHE activity was assayed by measuring the initial rate of Na(+)-dependent pH(i) recovery from an acid load imposed by prior lumen and bath Na(+) removal. Removal of Na(+) from the bath resulted in a significant, DIDS-insensitive, ethylisopropyl amiloride (EIPA)-inhibitable decrease in pH(i). This basolateral transporter showed very low affinity for EIPA and Hoechst 694 (IC(50) = 9.0 and 247 microM, respectively, consistent with NHE4). The recently reported apical NHE was more sensitive to inhibition by these drugs (IC(50) = 0.86 and 7.6 microM, respectively, consistent with NHE2). Increasing osmolality, a known activator of NHE4, greatly stimulated basolateral NHE. Immunohistochemical studies using antibodies against NHE1-4 peptides demonstrated expression of NHE2 along the apical and NHE4 along the basolateral, membrane, whereas NHE1 and NHE3 were not detected. These results suggest that macula densa cells functionally and immunologically express NHE2 at the apical membrane and NHE4 at the basolateral membrane. These two isoforms likely participate in Na(+) transport, pH(i), and cell volume regulation and may be involved in tubuloglomerular feedback signaling by these cells.

Luminal NaCl delivery regulates basolateral PGE2 release from macula densa cells

“…Individual cTAL's containing the MD segment with attached glomeruli were dissected from rabbit kidneys and perfused in vitro using methods similar to those described previously (17). For these biosensor studies, the cTAL containing the MD plaque was dissected away from the glomerulus, so that the basolateral surface of MD cells was accessible from the bath ( Figure 1).…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…NHE1 is present in most mammalian cells, notable exclusions are the macula densa, α-and β-intercalated cells of the kidney [133,16]. Consequently, NHE1 is often referred to as the «housekeeping» NHE isoform.…”

“…Interestingly they otherwise lack an overt renal or gastrointestinal phenotype, despite significant NHE2 expression in both these tissues [87,86,151]. Given the clear presence of NHE2 activity in the macula densa and distal convoluted tubule [133,152] more detailed studies on the renal phenotype have been performed. NHE2 KO mice display increased renal and plasma renin levels [59].…”

Identification and subcellular localization of the Na+/H+ exchanger and a novel related protein in the endocrine pancreas and adrenal medulla

“…NHE2 and NHE3 are mainly found at the apical pole of epithelial cells in kidney (Chambrey et al 1998), intestine (Chu et al 2002) and duct cells of salivary glands and pancreas (Lee et al 1998(Lee et al , 2000, where they play a role in Na C and fluid absorption, and secretion of protons (Orlowski & Grinstein 2004). NHE4 has been identified in the macula densa of the kidney (Peti-Peterdi et al 2000) and in the stomach (Rossmann et al 2001). NHE5 has mainly been found in the brain where it seems to behave like NHE3 (Baird et al 1999).…”