Relationships between the effects of superoxide anion and palmitoyl-L-carnitine on the Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum.

In order to understand interactions between oxidants and non-antioxidants, relationships between the effects of superoxide anion radical (O2-) and palmitoyl-L-carnitine (PLC) on the Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum were studied. PLC was ineffective in preventing the reduction of ferricytochrome c by O2-, suggesting that it has no O2(-)-scavenging properties. PLC exhibited a biphasic effect on Ca(2+)-ATPase activity, causing stimulation at low concentrations (3-10 microM) and inhibition at higher concentrations (30-1000 microM). The stimulatory effect on Ca(2+)-ATPase caused by 10 microM PLC was completely counteracted by O2-, whereas the stimulatory effect of L-cysteine (2 mM) was only diminished partially. Additive effects of PLC and L-cysteine attenuated the inhibitory effect of O2-, however, this appears to be due to L-cysteine alone. These results demonstrate that O2- can inhibit stimulatory effects of PLC on the Ca(2+)-ATPase, however, PLC does not block the inhibitory effect of O2-. Understanding interactions between oxidants/antioxidants and non-antioxidants at their cellular target proteins may provide essential information in the search for prevention of free radical injury.