Verapamil impairs human neutrophil chemotaxis by a non-calcium-mediated mechanism

The in vitro effect of pharmacologic concentrations (10(-8) to 10(-6) mol/L) of verapamil on human neutrophil migration and response to chemotactic signals was examined. Human neutrophils were preincubated (15 minutes) in verapamil and then assayed for chemotactic response to formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) (10(-8) mol/L). Cell viability was not affected by verapamil treatment. Verapamil-treated cells displayed 40% to 50% reductions in directed migration at all concentrations (P less than 0.02). Activated random migration (chemokinesis) was also impaired by verapamil treatment, but random locomotion was not affected except at a high concentration (10(-6) mol/L). This pharmacologic action of verapamil was not rapidly reversible by washing cells free of drug, but it was necessary that cells be exposed to drug before the chemotactic signal. In addition to f-Met-Leu-Phe, chemotactic response to activated human serum was also reduced for neutrophils. Several experiments were conducted to determine whether verapamil affected neutrophils as a calcium antagonist. Calcium antagonist binding-site assays using radiolabeled dihydropyridines provided no evidence for the presence of calcium channels in neutrophil membranes. Also, 45Ca2+ uptake assays demonstrated increased uptake of 45Ca2+ by f-Met-Leu-Phe-stimulated neutrophils, but no effect on uptake by verapamil exposures (10(-6) mol/L). Finally, the cytosolic calcium-chelating dye, quin 2 acetomethoxy ester (quin 2), was used as a fluorescent indicator to measure cytosolic Ca2+ concentrations, [Ca2+]i, in neutrophils. Verapamil exposures over a wide concentration range (10(-6) to 10(-4) mol/L) did not affect resting [Ca2+]i or [Ca2+]i transients after f-Met-Leu-Phe (10(-8) mol/L) stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)