In vitro modulation of human neutrophil superoxide anion generation by various calcium channel antagonists used in ischemia-reperfusion resuscitation

Generation of toxic oxygen species by activated polymorphonuclear leukocytes (PMNs) may represent an important mechanism of ischemia-reperfusion injury. Concentration-response data concerning inhibition of superoxide anion (O2-) generation by NADPH oxidoreductase (NADPH OR) from isolated human PMN were generated for five calcium channel antagonists commonly utilized in ischemia-reperfusion investigational therapeutics. Regression analysis derived IC50 values for verapamil, nimodipine, nicardipine and lidoflazine were 45, 20, 12 and 7 microM respectively. Inhibition of the extent of reaction at 5 min paralleled inhibition of initial velocity. No inhibition by flunarizine was noted at concentrations less than or equal to 25 microM (where it did not alter reaction mixture composition). Only nicardipine demonstrated a significant concentration-response effect relative to prolonging lag time preceding O2- synthesis. Inhibition appeared at least partially reversible for all five agents. Neither PMN activation/desensitization, free-radical scavenging, nor PMN cytotoxicity appeared to be involved in the inhibition of PMN O2- synthesis by these agents. Ca2+ antagonist inhibition of PMN NADPH OR appears to involve more than simple inhibition of Ca2+ flux across the PMN plasma membrane. Direct inhibition of the intracellular events involved in the activation and/or activity of NADPH OR may be operative.