Isoforms of Na+, K+-ATPase in human prostate; specificity of expression and apical membrane polarization

Abstract

The cellular distribution of Na+, K+-ATPase subunit isoforms was mapped in the secretory epithelium of the human prostate gland by immunostaining with antibodies to the α and β subunit isoforms of the enzyme. Immunolabeling of the α1 , β1 and β2 isoforms was observed in the apical and lateral plasma membrane domains of prostatic epithelial cells in contrast to human kidney where the α1 and β1 isoforms of Na+, K+- ATPase were localized in the basolateral membrane of both proximal and dista1 convoluted tubules. Using immunohistochemistry and PCR we found no evidence of Na+, K+-ATPase α2 and α3 isoform expression suggesting that prostatic Na+, K+-ATPase consists of α1/β1 and α1/β2 isozymes. Our immunohistochemical findings are consistent with previously proposed models placing prostatic Na+, K+-ATPase in the apical plasma membrane domain. Abundant expression of Na+, K+- ATPase in epithelial cells lining tubulo-alveoli in the human prostate gland confirms previous conclusions drawn from biochemical, pharmacological and physiological data and provides further evidence for the critica1 role of this enzyme in prostatic cell physiology and ion homeostasis. Na+, K+-ATPase most likely maintains an inwardly directed Na+ gradient essential for nutrient uptake and active citrate secretion by prostatic epithelial cells. Na+, K+-ATPase may also regulate lumenal Na+ and K+, major counter-ions for citrate.