2 EFFECTS OF LYSOPHOSPHATIDIC ACID ON CA2-MOVEMENT IN CULTURED BOVINEADRENAL CHROMAFFIN CELLS()

We found that lysophosphatidic acid (LPA) exerted two effects on Ca2+- movement in cultured bovine adrenal chromaffin cells. At concentration s of above 10(-5) M, it induced slight, but significant Ca-45(2+) infl ux, resulting in release of a small portion of stored catecholamine. A t high concentrations it also significantly increased the intracellula r Ca2+ concentration in Fura-2-loaded cells. At concentrations as low as 10(-7) M, it stimulated extracellular Na+-dependent Ca-45(2+) efflu x, possibly by increasing Na+/Ca2+ exchange. The maximal efflux of Ca2 + attained with 10(-5) M LPA was inhibited by tyrosine kinase inhibito rs, but augmented by a protein kinase C inhibitor. These results sugge st that LPA-induced Ca2+ efflux is controlled positively and negativel y by mechanisms involving tyrosine kinase and protein kinase C, respec tively.