Mobilisation of arachidonic acid in human A431 cells in the presence of epidermal growth factor, calcium ions, and cyclic AMP.

Epidermal growth factor (EGF) at a concentration of 5 x 10(-11)-10(-8) M invoked mobilisation of arachidonate in cultured A431 human epidermal carcinoma cells and release of a certain proportion of free arachidonic acid and its derivatives into the growth medium. At a concentration of 2 x 10(-8)-4 x 10(-5) M, Ca2+ ions enhanced mobilisation of arachidonate and induced virtually total release of arachidonic acid and its derivatives into the medium. EGF at a concentration of 10(-8) M and Ca2+ ions at a concentration of 2 mM in the presence of calcium ionophore A23187 were found to have an additive effect on the release of arachidonic acid. Release of arachidonic acid by Ca2+ ions was inhibited by 30%-50% in the presence of 10(-4) M dibutyryl-cAMP (Bt2cAMP), isoproterenol, or noradrenaline. There was a 35%-55% increase in the release of arachidonate elicited by 10(-8) M EGF in the presence of 10(-4) M Bt2cAMP, noradrenaline, or isoproterenol. It is concluded that A431 cells contain two independent pathways for the mobilisation of arachidonic acid: a Ca(2+)-dependent pathway and an EGF-dependent pathway.