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The mechanisms underlying cytoplasmic pH (pH ;) regulation in rat thymic lymphocytes were studied using trapped fluorescein derivatives as pHi indicators . Cells that were acid-loaded with nigericin in choline + media recovered normal pH ; upon addition of extracellular Na'

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Summary. The disulfonic acid stilbene derivative SITS reported to l:~e covalently bonded to the membrane of the red blood cell, was found to be largely reversibly bound. Reversal of its specific inhibitory effect on anion permeability was attained by washing the cells with buffer containing albumin. The small fraction of covalently bonded SITS could be increased by prolonging the time of exposure of the cells or by multiple exposures. A series of other disulfonie stilbene derivatives was synthesized. All of them specifically inhibited anion permeability whether or not they are capable of forming covalent bonds. Their inhibitory effectiveness, however, varied over a 5,0~3-fold range, allowing certain conclusions to be made concerning the chemical architecture of the binding site. Certain of the compounds were almost entirely covalently bonded. One of them was labeled with 12sI and used to determine to which membrane proteins the compound is bound. Over 90 % was found in a protein band on acrylamide gels of 95,000 tool wt. The most effective compound against sulfate permeability was equally effective against chloride permeability, producing a maximum inhibition of over 95 %. The residual anion fluxes respond differently to pH and temperature than do the fluxes of unmodified cells.The permeability of the red blood cells to anions and to cations can be modified by a large variety of chemical agents (Passow, 1969;Deuticke,

A B $ T R A C T The conductive (net) anion permeability of human red blood cells was determined from net KC1 or KzSO4 effluxes into low K ÷ media at high valinomycin concentrations, conditions under which the salt efflux is limited primarily by the net anion permeability. Disulfonic stilbenes, inhibitors of anion exchange, also inhibited KCI or K2SO4 efflux under these conditions, but were less effective at lower valinomycin concentrations where K ÷ permeability is the primary limiting factor. Various concentrations of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) had similar inhibitory effects on net and exchange sulfate fluxes, both of which were almost completely DIDS sensitive. In the case of Cl-, a high correlation was also found between inhibition of net and exchange fluxes, but in this case about 35% of the net flux was insensitive to DIDS. The net and exchange transport processes differed strikingly in their anion selectivity. Net chloride permeability was only four times as high as net sulfate permeability, whereas chloride exchange is over 10,000 times faster than sulfate exchange. Net OHpermeability, determined by an analogous method, was over four orders of magnitude larger than that of CI-, but was also sensitive to DIDS. These data and others are discussed in terms of the possibility that a common element may be involved in both net and exchange anion transport.