Effects of calmodulin antagonists on calcium pump and cytosolic calcium level in human neutrophils

Abstract

The concentration of cytosolic free calcium was monitored in suspensions of intact human neutrophils in phosphate-buffered saline by means of the fluorescent indicator Indo 1 trapped in the cytosol. Trifluoperazine and n-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide markedly reduced the amplitude of the transient increase in cytosolic Ca2+ triggered by CaCl2 as well as by N-formyl-methionyl-leucyl-phenylalanine. The effect of the calmodulin antagonists on the calcium burst observed upon cell activation was much more pronounced in the presence of extracellular free calcium than in EGTA-containing media; it was not inhibited by wortmannin or thapsigargin. Nevertheless, trifluoperazine and n-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide inhibited the plasma-membrane Ca2+ ATPase if added to plasma membrane-enriched fractions of neutrophils. These results suggest that calmodulin antagonists affect calcium ion influx even if they inhibit plasma membrane Ca2+ ATPase.