Calmodulin content in rabbit reticulocyte and the influence of opioid peptides on calmodulin activity in its membrane.

Calmodulin (CaM) content in rabbit reticulocyte and the influence of opioid peptides on CaM activity in its membrane were studied by a highly sensitive assay of CaM activity based on the stimulation of Calcium-dependent phosphodiesterase activity. The CaM contents in reticulocytes were higher than those in normal erythrocytes, both in the cytosol fraction and in the membrane fraction. Among the opioid peptides, beta-endorphin (beta-EP) and dynorphin-A-(1-13) (dyn) had a significant inhibitory effect on CaM activity in reticulocyte membrane. The effect was not antagonized by naloxone or Mr. 2266, nor influenced by increase of Ca2+ concentration, but was reversed by the addition of exogenous CaM. This implies that the action of beta-EP and dyn on reticulocyte membranes probably involves an non-opioid mechanism, in which CaM may be an important key of linkage.