Abstract
We previously observed Ca 2+ release from intracellular Ca 2+ stores caused by reduction in extracellular Na + concentration ([Na +] o) (1). The purpose of this study was to determine whether lowering [Na +] o can elicit Ca 2+ release from Ca 2+ stores via the Na +/Ca 2+ exchanger and to elucidate the mechanisms related to the Ca 2+ release pathway in cultured longitudinal smooth muscle cells obtained from guinea pig ileum. Low [Na +] o-induced Ca 2+ release was inhibited by antisense oligodeoxynucleotides for Na +/Ca 2+ exchanger type 1 (anti-NCX). Application of anti-NCX to cells attenuated both the number of Ca 2+ responding cells and the expression of the exchanger. Moreover, microinjection of heparin, a blocker of inositol 1,4,5-trisphosphate (IP 3) receptors, into the cells inhibited low [Na +] o-induced Ca 2+ release. These findings suggest that low [Na +] o-induced Ca 2+ release occurs through an IP 3-induced Ca 2+ release mechanism due to changes in the Ca 2+ flux regulated by the Na +/Ca 2+ exchanger.
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