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

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.