Regional Distribution of Na,K-ATPase Activity in Porcine Lens Epithelium

Abstract

Na,K-ATPase activity is significantly higher at the equatorial region of the epithelium compared with the anterior, even though the level of Na,K-ATPase protein is similar in the two regions. It is possible that nonuniform distribution of functional Na,K-ATPase activity contributes to the driving force for circulating solute movement through the lens fiber mass.

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“…The activity of the pump is higher in the epithelium than other parts of the lens. 81 Functioning Na/K ATPase in epithelial cells is most important to keep lens fiber homeostasis. 82 When such homeostasis fails, cataract occurs.…”

Interaction between Connexin50 and Mitogen-activated Protein Kinase Signaling in Lens Homeostasis

“…Na ϩ is driven across fiber cell membranes by its electrochemical gradient, and in the fiber cytoplasm the direction of flow is reversed, with the current moving back toward the lens surface through gap junction channels (Mathias et al, 2007). Because the coupling of differentiating fibers is normally highest at the equator and lowest at the poles (Baldo and Mathias, 1992), the intercellular current is directed to the equatorial epithelium where Na ϩ /K ϩ -ATPase activity is also concentrated (Gao et al, 2000;Candia and Zamudio, 2002;Tamiya et al, 2003), and sodium is pumped out of the lens to complete the circuit. Water and dissolved metabolites follow the Na ϩ current creating the microcirculatory system for the avascular lens.…”

AKT activation promotes PTEN hamartoma tumor syndrome–associated cataract development

“…The sodium current normally exits the lens through the equatorial epithelium, where Na + /K + -ATPase activity is concentrated (18). The increased Na + concentration measured within PTEN KO lenses may have resulted from a decrease in Na + /K + -ATPase activity, which in turn could be mediated by elevated PI3K signaling following Pten deletion.…”

“…Within the lens, Na + is driven by its electrochemical gradient to move into the fiber cells, where the direction of flow is reversed and the current flows back to lens surface through gap junction channels (15,17). Gap junction coupling is concentrated at the equator in peripheral fiber cells, directing the Na + current to the equatorial epithelium, where Na + /K + -ATPase activity pumps Na + out of the lens to complete the circulatory loop (18). Na + transport is coupled to fluid circulation, creating a microcirculatory system that carries nutrients to the fiber cells and allows removal of metabolic waste.…”