Effect of the antianginal drug bepridil on intracellular Ca2+ release and extracellular Ca2+ influx in human neutrophils

To understand more fully the effects of bepridil. an antiarrhythmic and antianginal drug, on myocardial ischemia-reperfusion injury and systemic immune responses, its effect on intracellular Ca2+ levels ([Ca2+](i)) in human neutrophils was investigated by using fura-2 as a fluorescent probe. Bepridil(10-200 muM) increased [Ca2+](i) in a concentration-dependent fashion. This signal was partly inhibited by removal of extracellular Ca2+. In a Ca'f-free medium, pretreatment with bepridil (100 muM) abolished the Ca2+ release induced by thapsigargin (1 muM). an endoplasmic reticulum Ca2+ pump inhibitor, and by carbonylcyanide m-chlorophenylhydrazone (2 muM), a mitochondrial uncoupler. Pretreatment with carbonylcyanide m-chlorophenylhydrazone and thapsigargin, respectively, partly inhibited bepridil-induced Ca2+ release. Addition of Ca2+ (3 mM) increased [Ca2+](i) after pretreatment with bepridil (100 muM) in a Ca2+-free medium. Bepridil (100 muM)-induced Ca2+ release was not altered when phospholipase C was inhibited by U73122 (2 muM) Both Ca2+ release and Ca2+ entry induced by bepridil (100 muM) were augmented by activating protein kinase C with phorbol 12-myristate 13-acetate(10 nM). and were suppressed by inhibiting protein kinase C with GF 109203)( (2 muM). Treatment with bepridil (10-20 muM) for 30 min increased the production of reactive oxygen intermediates (ROI) by more than 50%. Collectively, it was found that bepridil increased [Ca2+](i) concentration-dependently in human neutrophils by releasing Ca2+ from the endoplasmic reticulum, mitochondria and, possibly, other compartments in a phospholipase C-independent manner. Bepridil also activated Ca2+ influx. The activity of protein kinase C may regulate bepridil-induced Ca2+ release and Ca2+ entry. ((C)) 2001 Elsevier Science B.V. All rights reserved.