Thiol-dependent passive K+Cl− transport in sheep red blood cells: VI. Functional heterogeneity and immunologic identity with volume-stimulated K+(Rb+) fluxes

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Abstract
Summary Ouabain-resistant (OR), volume-or N-ethylmaleimide (NEM)-stimulated K+(Rb+)Cl− fluxes were measured in low-K+ sheep red cells and found to be functionally separate but immunologically similar. In anisosmotic solutions both K+ effluxes and Rb+ influxes of NEM-treated and control cells were additive. In contrast to the NEM-stimulated K+Cl− flux, metabolic depletion did not reduce K+Cl− flux of normal or swollen cells. The anion preference of OR K+ efflux in NEM-treated cells was Br−>Cl−>HCO −3 =F−≫I−=NO −3 =CNS−, and hence consistent with a reported Br−>Cl−>NO −3 sequence of the volume-dependent K+Cl− transport. Alloimmune anti-Ll antibodies known to decrease passive K+ fluxes in low K+ cells reduced by 51% both volume-and NEM-stimulated, furosemidesensitive Rb+Cl− fluxes suggesting their immunologic identity, a conclusion also supported by anti-L1 absorption studies. Since pretreatment with anti-L1 prevented the activation of Rb+ influx by NEM, and the impermeant glutathionmaleimide-I did not stimulate Rb+Cl− influx, the NEM reactive SH groups must be located apart from the L1 antigen either within the membrane or on its cytoplasmic face. A model is proposed consisting of a K+Cl− transport path(s) regulated by a protein with two functional subunits or domains; a chemically (C s) and a volume (V s)-stimulated domain, both interfacing with the L1 surface antigen. Attachment of alloanti-L1 from the outside reduces K+Cl− transport stimulated throughC s by NEM orV s by cell swelling.

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