Effects of lysophosphatidylcholine and arachidonic acid on the regulation of intracellular Ca2+ transport.

The role of lysophosphatidylcholine and arachidonic acid in signal transduction was investigated using subcellular organelles and permeabilized cells from liver. Both substances can be generated intracellularly by the action of phospholipase A2 on phosphatidylcholine. Lysophosphatidylcholine as well as arachidonic acid raised the free Ca2+ concentration in the incubation media of permeabilized cells, isolated mitochondria and microsomes. The half maximally effective concentrations for Ca2+ release from mitochondria were 78 +/- 1 mumol/l for lysophosphatidylcholine and 80 +/- 11 mumol/l for arachidonic acid. Though isolated microsomes released Ca2+ in response to both agents, the combined presence of mitochondria and microsomes did not exhibit a synergism in Ca2+ release in response to arachidonic acid; the increase in the free Ca2+ concentration in response to lysophosphatidylcholine was even smaller than with mitochondria alone. It is concluded that the two reaction products of phospholipase A2 can raise the cytoplasmic Ca2+ concentration and therefore may participate in cellular signal transduction.