Properties of chloride transport in barnacle muscle fibers.

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Abstract
Unidirectional 36Cl fluxes were measured in internally dialyzed barnacle giant muscle fibers. About 50-60% of the Cl efflux was irreversibly blocked by the amino-group reactive agent, 4-acetamido-4''-isothiocyano-stilbene-2,2''-disulfonic acid (SITS), when it was applied either intra- or extracellularly. Similarly, Cl influxes was also blocked by SITS. No significant effect on [Cl]i [intracellular concentration of chloride] of SITS was noted in intact muscle fibers. The rate of net Cl efflux from muscle fibers which were Cl-loaded by overnight storage at 6.degree. C could be slowed by SITS treatment. Two classes of anions were defined based upon their effects on Cl efflux. Methanesulfonate and nitrate inhibited Cl efflux either when they replaced external Cl or when they were added to a constant external Cl concentration. The other group of anions (propionate, formate) stimulated both Cl efflux and influx and such stimulation could be blocked by SITS. Propionate influx was not nearly as large as the stimulated Cl efflux and was unaffected by SITS. Neither the effects of SITS nor those of the anion substitutes could be simply accounted for by changes in the membrane resting potential or conductance. A mediated transport system for Cl across the barnacle sarcolemma is suggested.