Two effects of lysophosphatidic acid on Ca(2+)-movement in cultured bovine adrenal chromaffin cells

We found that lysophosphatidic acid (LPA) exerted two effects on Ca(2+)-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 Na+/Ca2+ 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.