ANION-EXCHANGE IN TYPE-II PNEUMOCYTES FRESHLY ISOLATED FROM ADULT GUINEA-PIG LUNG

We have studied chloride influx and efflux in a highly purified prepar ation of type II cells freshly isolated from adult guinea-pig lung usi ng Cl-36(-). Chloride uptake was time-dependent, saturable (K-m < 10 m M) and was inhibited by 4,4'-diisothiocyanatostilbene-2,2'disulphonic acid (DIDS; K-i approximate to 80 mu M). In the absence of external ch loride (substituted by gluconate), Cl-36(-) uptake exhibited an oversh oot above equilibrium. The rate of Cl-36(-) entry was strongly inhibit ed by addition of external nitrate; sulphate was a weaker inhibitor. C l-36(-) efflux was stimulated by external bromide > bicarbonate greate r than or equal to chloride greater than or equal to citrate; and was inhibited by proprionate > acetate > oxalate. Although the ''chloride channel blocker'' 4-nitro-2-(3-phenylpropylamino)benzoate (0.14 mM) ca used an inhibition, Cl-36(-) influx did not appear to be electrogenic. These data are compatible with the existence of a substantial electro neutral anion-exchange pathway for chloride transport in freshly isola ted adult type II pneumocytes.