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

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 alpha and beta subunit isoforms of the enzyme. Immunolab eling of the alpha1, beta1 and beta2 isoforms was observed in the apical an d lateral plasma membrane domains of prostatic epithelial cells in contrast to human kidney where the alpha1 and beta1 isoforms of Na+, K+-ATPase were localized in the basolateral membrane of both proximal and distal convolut ed tubules. Using immunohistochemistry and PCR we found no evidence of Na+, K+-ATPase alpha2 and alpha3 isoform expression suggesting that prostatic N a+, K+-ATPase consists of alpha1/beta1 and alpha1/beta2 isozymes. Our immun ohistochemical findings are consistent with previously proposed models plac ing 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 biochemic al, pharmacological and physiological data and provides further evidence fo r the critical role of this enzyme in prostatic cell physiology and ion hom eostasis. Na+, K+-ATPase most likely maintains an inwardly directed Na+ gra dient essential for nutrient uptake and active citrate secretion by prostat ic epithelial cells. Na+, K+-ATPase may also regulate lumenal Na+ and K+, m ajor counter-ions for citrate.