Expression and regulation of Na,K-ATPase in primary culture of proximal tubule cells

We previously reported that butyrate slowed the downregulation of activities of differentiation marker enzymes for the proximal tubule during cellular proliferation. This work was designed to delineate whether butyrate also regulated activity of Na,K-ATPase, a basolateral membrane marker. We observed that Na,K-ATPase activity was decreased in cultured proximal tubule cells, which occurred before cell proliferation. When cultured proximal tubule cells approached confluency from day 4 to day 6. Na,K-ATPase activity was increased by 27%, but the increase was not seen in cultures under a lower plating density. Cultured proximal tubule cells under a large plating density also exhibited greater Na,K-ATPase activity than those under a small density. Na butyrate inhibited Na,K-ATPase activity throughout the course of primary culture and dependent on dose in the range 2-5 mM. At the confluent phase, 24-h treatment of butyrate (5mM) induced a 24% decrease in Na,K-ATPase activity, which is associated with coordinated decreases in both Na,K-ATPase α and β subunit abundances and is mediated by coordinate decreases in both Na,K-ATPase α and β mRNA levels. Moreover, Na butyrate, at a dose greater than 2 mM, inhibits proliferation of proximal tubular cells, but results in cell hypertrophy. Finally, the effect of butyrate on cell growth and Na,K- ATPase expression cannot be mimicked by other short chain fatty acids, such as acetate, hexanoate or octanoate.