Identification of a Pool of Non-pumping Na/K-ATPase

Abstract

Recent studies have ascribed many non-pumping functions to the Na/K-ATPase. Here, we present experimental evidence demonstrating that over half of the plasma membrane Na/KATPase in LLC-PK1 cells is performing cellular functions other than ion pumping. This "non-pumping" pool of Na/K-ATPase, like the pumping pump, binds ouabain. Depletion of either cholesterol or caveolin-1 moves some of the "non-pumping" Na/KATPase into the pumping pool. Graded knock-down of the ␣1 subunit of the Na/K-ATPase eventually results in loss of this "non-pumping" pool while preserving the pumping pool. Our prior studies indicate that a loss of the non-pumping pool is associated with a loss of receptor function as evidenced by the failure of ouabain administration to induce the activation of Src and/or ERK. Therefore, our new findings suggest that a substantial amount of surface-expressed Na/K-ATPase, at least in some types of cells, may function as non-canonical ouabain-binding receptors.

Expression of Mutant α1 Na/K-ATPase Defective in Conformational Transition Attenuates Src-mediated Signal Transduction*

“…However, the pumping activities in the I3 and F19 cells were much higher than that of parental PY-17 cells (19).…”

Involvement of Reactive Oxygen Species in a Feed-forward Mechanism of Na/K-ATPase-mediated Signaling Transduction

“…Both PY-17 and C2-9 cells have disrupted Na/K-ATPase⅐c-Src signaling and do not respond to ouabain stimulation in terms of c-Src activation (11,31,32). As shown in Fig.…”

Endogenous digitalis: pathophysiologic roles and therapeutic applications

“…94 Some studies have not found major differences in ouabain affinity between the caveolar and the non-caveolar Na + /K + -ATPase. 47 We have observed, however, that in renal proximal tubular epithelial cells both ouabain-induced signal transduction through the Na + /K + -ATPaseSrc-EGFR cascade and ouabain-induced clathrin-mediated endocytosis of the Na + /K + -ATPase were limited to the Na + /K + -ATPase residing in caveolae. 95,96 These discrepancies might be explained by different levels of expression of the γ subunit of the Na + /K + -ATPase in the preparations employed, as suggested by Nguyen and co-workers.…”