Guinea pig peritoneal macrophages were treated with saponin, and the effects of calmodulin and 'calmodulin antagonists' on the Ca2+ uptake of saponin-treated macrophages were examined. With this intracellular Ca2+-accumulating system we found that intact macrophages contained 672 ng/4 X 106 cells (2874 ng/mg of protein), which was reduced to 64 ng/4 X 106 cells (799 ng/mg of protein) by treatment of the macrophages with saponin. Exogeneously added calmodulin affected neither the maximal capacity of the Ca2+ uptake nor the apparent affinity of Ca2+ of the saponin-treated macrophages. All of the calmodulin antagonists examined [chlorpromazine, trifluoperazine, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, and N-(6-aminohexyl)-1-naphthalenesulfonamide] inhibited the Ca2+ uptake of saponin-treated macrophages. However, the concentrations of these drugs required for half-maximal inhibition of the Ca2+ uptake were much higher than those described for the calmodulin stimulation of phosphodiesterase. Troponin I, which inhibited calmodulin-stimulated phosphodiesterase activity, did not inhibit Ca2+ uptake. Inhibition of Ca2+ uptake by chlorpromazine and trifluoperazine was not reduced by the addition of excess calmodulin and was not altered by changes in concentration of both Mg-ATP and free Ca2+. The Ca2+ accumulated in saponin-treated macrophages was released by the addition of chlorpromazine and trifluoperazine, and, after removal of the drugs, Ca2+ accumulation was restored. This release of Ca2+ by chlorpromazine and trifluoperazine was concentration-dependent, and the concentration required for half-maximal release of Ca2+ was similar to that for half-maximal inhibition of Ca2+ uptake. From these findings, we conclude that the intracellular Ca2+-accumulating system in guinea pig peritoneal macrophages was not stimulated by calmodulin. Although calmodulin antagonists inhibited Ca2+ uptake and released accumulated Ca2+ in saponin-treated macrophages, these effects may be unrelated to the specific effect of the drugs on calmodulin.
|Number of pages||8|
|Publication status||Published - Jan 1 1983|
All Science Journal Classification (ASJC) codes
- Molecular Medicine