Na+-K+-ATPase expression. A. The Na+-K+-ATPase is highly expressed in the pronephric ducts and entirely localized to the lateral and highly invaginated basolateral cell membranes. B. Na+-K+-ATPase expression in duct counterstained with DAPI. Images are three-dimensional reconstructions of the original CLSM z-series, showing a median longitudinal section of the pronephric duct.