STILBENEDISULPHONATES INHIBITAPPARENTLY SEPARATE CHLORIDE TRANSPORTERS INSKELETAL MUSCLE OF RANA TEMPORARIA

SUMMARY 1.Inhibition of36Cl- efflux infrog muscle bythestilbene disulphonates (SD)SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-dis ulphonate) andDNDS (4,4'-dinitro-stilbene-2,2'-disulphonate) depends ontheexternal pH,while theblocking ofClconductance withSITSisindependent ofpH.The36Cl- efflux inhibition withDNDS hasbeenstudied inthindepolarized musclefibre bundles inordertoexamine whether this difference isconsistent withonetransporter orreflects theexistence of two mutually independent conductive andnon-conductive SD-sensitive Clpathways. 2.The36Cl- efflux response toasudden inward KClgradient wasstudied. Athigh pHtheefflux decreased aspredicted fordominant conductive Cl-single-filing, andat lowpH theefflux increased inagreement withdominant non-conductive Clantiport. DNDS inhibition resulted inthesameresponse, anefflux decrease, atboth highandlowpH,suggesting aselective reduction ofthenon-conductive contribution atlowpH. 3.Theinhibition of36Cl- efflux asafunction oftheDNDS concentration atan external pHof6-9showedcomplex kinetics, whichcould bedescribed asthesumof twoMichaelis-Menten functions withdifferent half-inhibition concentrations of DNDS. 4.Theresults support thehypothesis thatthestilbene disulphonate-sensitive Cltransport ismediated bytwoseparate transporters rather thanone.