POLARIZED DISTRIBUTION OF KEY MEMBRANE-TRANSPORT PROTEINS IN THE RAT SUBMANDIBULAR-GLAND

Immunofluorescence labelling and confocal microscopy were employed to examine the polarized distribution of several membrane transport prote ins believed to be essential for salivary secretion in the rat submand ibular gland. The Na+/K+-ATPase, Na+/H+ exchanger isoform 1 (NHE1), an d the secretory Na+/K+/2Cl(-) cotransporter isoform were all found in the basolateral membranes of acinar and intralobular duct cells. Anion exchanger isoform 2 (AE2) was found only in the basolateral membranes of acinar cells, while AE1 was absent from glandular epithelial cells . Aquaporin 5 was detected in the apical membranes of acinar cells, wh ile the cystic fibrosis transmembrane conductance regulator was found only in apical membranes of intralobular duct cells. NHEs 2 and 3 were found in the apical membranes of both acinar and intralobular duct ce lls. Our results are generally consistent with the expected distributi on of most transporters based on previous physiological and pharmacolo gical experiments. However, the epical localization of NHEs 2 and 3, a nd the presence of the secretory isoform of the Na+/K+/2Cl(-) cotransp orter in intralobular duct cells were not predicted.