Effect of sodium on cellular calcium transport in rat kidney

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Abstract
Summary The influence of extracellular Na (Na o ) on cellular Ca transport and distribution was studied in rat kidney slices. Calcium efflux from prelabeled slices was depressed when Na o was completely replaced by choline or tetraethylammonium (TEA) ions and it was markedly stimulated when Na was reintroduced in a Na-free medium. However, reducing Na o (with choline or TEA as substituting ions) did not increase the total slice40Ca, their total exchangeable Ca pool, or the40Ca or45Ca of mitochondria isolated from these slices. Kinetic analyses of steady-state45Ca desaturation curves showed that reducing Na o depressed the exchange of Ca across the plasma membrane, slightly decreased the cytosolic Ca pool, but did not significantly affect the mitochondrial Ca pool and Ca cycling. Ouabain (10−3 m) which should reduce the Na gradient across the plasma membrane had no effect on calcium distribution and transport. These results suggest that in kidney cells low Na o depresses Ca influx as well as Ca efflux; there may be an interaction between Na and Ca at a possible carrier located in the plasma membrane, but there is no Na/Ca exchange as described in several excitable tissues.

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