Inhibition of the Anion Permeability of Sarcoplasmic Reticulum Vesicles by Some Stilbene Derivatives

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Abstract
This paper concerns a study of the inhibition of sulfate permeability of sarcoplasmic reticulum vesicles by stilbene derivatives, such as 4-acetoamido-4'-isothiocyano-2,2'-stilbene-disulfonic acid (SITS), 4, 4'-diisothiocyano-stilbene-2, 2'-disulfonic acid (DIDS), and diisothiocyano-1, 2-diphenyl-ethane-2, 2'-disulfonic acid (H 2 DIDS). The level of sulfate permeability was measured by using a radioactive tracer. The sulfate efflux curves comprise two phases. This is explained by the existence of two types of vesicles with different permeability. The permeability of the rapidly permeated vesicles was at least 100 times higher than that of the slowly permeated vesicles. The permeability of both types of vesicles was inhibited by the above inhibitors. Apparent dissociation constants for the inhibitors of sulfate permeability were 5 μM, 6 μM, and 40 μM for DIDS, H 2 DIDS, and SITS, respectively. The relation between sulfate permeability and the amount of the bound inhibitors was studied. To effect complete inhibition of permeation by sulfate in both vesicles, the binding of 5 μmol of inhibitors/g protein was required. However, kinetic analysis of the sulfate efflux of the rapidly permeated vesicles suggested that the amount of the anion transport system is much smaller than 5 μmol/g protein. Permeability for Na + and choline was not affected by the same concentration of inhibitors. However, Ca 2+ permeability was increased by the inhibitors, and at the same time Ca 2+ uptake was reduced. This inhibition of Ca 2+ uptake was explained by the increase of Ca 2+ permeability.

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