Sodium entry routes in principal and intercalated cells of the isolated perfused cortical collecting duct

Abstract

Transmembrane sodium transport pathways were studied in principal and intercalated cells of the isolated perfused rabbit cortical collecting duct. Intracellular electrolyte concentrations in individual collecting duct cells were measured by electron microprobe analysis during blockage of basolateral Na-K-ATPase by ouabain and simultaneous inhibition of sodium entry across the apical and/or basolateral cell membrane. In principal cells the ouabain-induced rise in cell sodium concentration could only partially be blocked by amiloride (10(-4) mol/l) in the perfusion fluid. Amiloride (10(-3) mol/l) added to the bathing solution produced a further, significant reduction of sodium influx. In principal cells the ouabain-induced increase in sodium concentration was completely prevented by amiloride in the perfusion solution in combination with omission of sodium from the peritubular bathing solution. In intercalated cells ouabain caused a less pronounced increase in sodium concentration than in principal cells. Neither amiloride in the perfusate, nor amiloride in both bathing and perfusion solution, significantly reduced the ouabain-induced rise in intercalated cell sodium concentration. These results indicate that in principal cells amiloride-sensitive sodium channels constitute the predominant pathway for sodium entry across the apical cell membrane. In addition, substantial amounts of sodium enter principal cells across the basolateral cell membrane, probably via Na-H exchange. Finally, the data suggest that in intercalated cells sodium channels and the Na-H exchange are sparse or even absent.

Correlation between Intracellular Activities of Ca²⁺ and Na⁺ in Rat Cortical Collecting Duct – A Possible Coupling Mechanism between Na⁺-K⁺-ATPase and Basolateral K⁺ Conductance

“…Measurements of [Na ] of principal cells of the CCD are available only from electron microprobe analysis from rabbit kidney [18][19][20]. In these studies, [Na ], of 10 mmol/ kg wet weight was found under basal conditions in CCD from rabbits or rats fed a normal-Na diet.…”

Cell-specific regulation of L-WNK1 by dietary K+

“…Whereas PCs possess robust basolateral Na ϩ -K ϩ -ATPase activity (3,8,63,71,78), the density of conducting and immunoreactive apical BK channels in these cells is low compared with ICs (17,27,44,59,62,63,68,77,89,100), suggesting that PCs might not be responsible for FIKS. In contrast to PCs, functional and immunoreactive BK channels are abundant in the apical membrane of ICs (17, 27, 44, 59, 62, 63, 68, 77, 100).…”

“…In contrast to PCs, functional and immunoreactive BK channels are abundant in the apical membrane of ICs (17, 27, 44, 59, 62, 63, 68, 77, 100). These cells presumably sustain FIKS via basolateral Na ϩ -K ϩ -Cl Ϫ cotransporter-mediated K ϩ uptake (46), since they possess little basolateral Na ϩ -K ϩ -ATPase activity (3,8,63,71,78). In animals fed a high-K ϩ diet, net K ϩ secretion in the ASDN is markedly enhanced, along with an increase in ROMK expression in PCs and BK expression in ICs (44,59,64,94).…”

Role of NKCC in BK channel-mediated net K+secretion in the CCD

“…In rabbit kidney, Na ϩ -K ϩ -ATPase antigenicity has been identified along the basolateral membrane of intercalated cells (54). However, electron microprobe analysis of intracellular electrolyte concentrations in individual cells in isolated, perfused rabbit CCDs revealed a significantly smaller increase in [Na] i in intercalated vs. principal cells exposed to basolateral ouabain (65). In sum, these data suggest that intercalated cells may not have sufficient Na ϩ -K ϩ -ATPase activity to sustain high rates of luminal K ϩ secretion.…”