Characteristics of arachidonic-acid-mediated brain protein kinase C activation: evidence for concentration-dependent heterogeneity.

Arachidonic acid (AA) activates brain protein kinase C (PKC) in a specific manner, and which differs from that of diacylglycerol (DG)-mediated PKC activation in cofactor Ca2+ and phosphatidylserine (PtdSer) requirements. We presently report that characteristics of AA-mediated activation are heterogenous, and are dependent upon the concentrations of AA. Highly sensitive PKC activation (HS) occurring at concentrations of 20 microM AA can be distinguished from less sensitive PKC activation (LS) requiring concentrations of at least 160 microM AA, on the basis of the effects of phorbol ester TPA or DG, phosphatidylcholine (PtdCho) and sodium deoxycholate (DOC). TPA, like DG suppressed the HS reaction whereas it enhanced the LS reaction. PtdCho, a phospholipid which does not affect DG-mediated activation, also prevented the HS reaction without affecting the LS reaction. This latter was inhibited at 100 microM DOC, a concentration which slightly stimulated the HS reaction. The substrate specificity was also different in the two reactions: the preferential substrate for PKC in HS was histone type VII-S, while it was histone type V-S in LS. Both reactions were similarly affected by PtdSer. In 0.1 mM CaCl2, PtdSer stimulated AA-mediated activation without evoking additive responses while this phospholipid prevented this activation in 0.5 mM EGTA, suggesting that AA and PtdSer bind PKC on the same or related sites. Together these results provide evidence for the existence of different modes of AA-mediated PKC activation with unique characteristics which presumably involve two different binding sites for AA on the same molecule and/or different PKC isoforms.