IDENTIFICATION AND PROPERTIES OF PATHWAYS FOR K-PIG AND RAT ALVEOLAR EPITHELIAL TYPE-II CELLS( TRANSPORT IN GUINEA)

1. Rb-86(+) was used to study potassium uptake and efflux in type II p neumocytes freshly isolated from adult guinea-pig and rat lung. 2. Bot h species exhibited a substantial ouabain-sensitive component of potas sium influx. 3. In rats, most of the ouabain-resistant influx was abol ished by bumetanide and removal of extracellular chloride elicited no further effect. In contrast, only a proportion of the ouabain-insensit ive uptake was inhibitable by bumetanide in guinea-pigs and this speci es showed an additional component of influx, which was chloride depend ent and which was reduced by either the K+-H+-ATPase inhibitor, omepra zole, or by the stilbene derivative, 4,4'-diisothiocyanostilloene-2,2' -disulphonate (DIDS). The chloride-dependent component was also appare nt in efflux experiments in guinea-pigs, but was absent in rats. 4. Ou abain-insensitive ATPase activity was assayed in highly purified apica l membranes from guinea-pig type II pneumocytes. This activity was inh ibitable by omeprazole (apparent inhibition constant, K-i, was similar to 40 mu M), was potassium dependent (apparent activation constant, K -a, was similar to 200 mu M) and was doubled by the addition of nigeri cin. 5. While potassium transport in rat type II cells is adequately a ccounted for by Na+-K+-ATPase and Na+-K+-2Cl(-) cotransport, our data suggest the additional presence of K+-Cl- cotransport and K+-H-+-ATPas e in guinea-pig type II pneumocytes. A model of how alveolar subphase acidification may occur is proposed.