Activity and activation of the granulocyte superoxide-generating system

Abstract

Phagocytic cells generate superoxide (O2-) as a part of the respiratory burst of phagocytosis. We studied human granulocyte O2- production in vitro in response to phorbol myristate acetate, a soluble fatty acid ester that stimulates O-2 generation. The properties of this compound permit the adaptation of a continuous of O2- production to the study of the activity and activation (i.e., the change from the active state) of the O2--generating system. The two processes, measured respectively as the rat of O2- production and the lag time for its attainment, respond differently to manipulations involving temperature, pH, phorbol myristate acetate concentration, N-ethyl maleimide inhibition, and energy metabolism. Changes in pH profoundly influence the rate without changing the lag time. Increase in temperature above 37°C depress the rate but continue to shorten the lag time. Thus, the activation and activity of the O2--generating system appear to have different pH and temperature dependency. In addition, they have different dose-response curves for phorbol myristate acetate stimulation: at high concentrations the rate reaches a plateau but the lag time continues to shorten. Activity of the human O2--generating system is sensitive to metabolic inhibitors, such as N-ethyl maleimide, 2-deoxyglucose, and the combination of 2-deoxyglucose with dinitrophenol or cyanide. The rate of activation (lag time) is unaffected by these compounds. These findings show that the activity of the human O2--generating system and its activation are separable processes. Furthermore, comparison of the above characteristics of human peripheral blood and guinea pig peritoneal exudate granulocytes reveals several important differences.