Transport of Inorganic Anions in Perfused Rat Liver

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Abstract
The transport of inorganic anions (sulfate, chloride, phosphate and bicarbonate) across the plasma membrane was investigated in hemoglobin-free perfused rat livers, applying the multiple-indicator dilution technique (pulse labelling of inorganic anions and indicator substances). The following results were obtained: 1 Chloride and phosphate exchanged very slowly between extracellular and intracellular spaces, whereas the exchange of sulfate was rapid. 2 The exchange of sulfate exhibited saturation kinetics with half-maximal rates at approximately 8 mM sulfate. The maximal steady-state exchange rate was near 60 μmol × min−1× (g liver wet wt)−1. 3 The exchange of sulfate was inhibited completely by cyanocinnamate; the inhibition was fully reversible. It was also completely, but irreversibly inhibited by diisothiocyanostilbenedisulfonic acid; the amount of the inhibitor bound by the liver that was required for half-maximal effect was considerably less than that required for the inhibition of d-lactate transport. 4 The exchange of sulfate was also inhibited by pyruvate and l-lactate at high concentrations; the inhibition was not competitive. 5 The exchange of d-lactate was not inhibited by sulfate or chloride. 6 Bicarbonate exchanges very rapidly; this process cannot be inhibited by cyanocinnamate. From these observations the following conclusions were drawn. A carrier system for the transport of inorganic anions, at least for sulfate, exists in the plasma membrane of liver. This carrier is specific for inorganic anions and is independent of the carrier system for the transport of monocarboxylates, in contrast to the findings with erythrocytes. Moreover, this carrier does not transport bicarbonate at a significant rate. Most likely, the rapid exchange of bicarbonate reflects the free diffusion of carbon dioxide.

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