(2) An action under ORS 646.780 to recover damages shall be commenced within four years after the cause of action accrued, or within one year after the conclusion of any proceeding based in whole or in part on the same matter complained of, filed either by the United States under the antitrust laws of the United States, except section 15a of Title 15 of the United States Code, or by the state (except in an action for damages by the state) under ORS 646.760, 646.770 or 646.780 (whichever is first concluded), whichever is later. [1975 c.255 §12]