Two effects of lysophosphatidic acid on Ca2+-movement in cultured bovine adrenal chromaffin cells

We found that lysophosphatidic acid (LPA) exerted two effects on Ca²⁺-movement in cultured bovine adrenal chromaffin cells. At concentrations of above 10⁻⁵ M, it induced slight, but significant ⁴⁵Ca²⁺ influx, resulting in release of a small portion of stored catecholamine. At high concentrations it also significantly increased the intracellular Ca²⁺ concentration in Fura-2-loaded cells. At concentrations as low as 10⁻⁷ M, it stimulated extracellular Na⁺-dependent ⁴⁵Ca²⁺ efflux, possibly by increasing $\text{Na}{}^{\mathrm{+}}\text{Ca}{}^{\mathrm{2+}}$ exchange. The maximal efflux of Ca²⁺ attained with 10⁻⁵ M LPA was inhibited by tyrosine kinase inhibitors, but augmented by a protein kinase C inhibitor. These results suggest that LPA-induced Ca²⁺ efflux is controlled positively and negatively by mechanisms involving tyrosine kinase and protein kinase C, respectively.