how this last step is accomplished is much debated , but the following possibilities are currently considered as the mechanisms responsible for cyclic amp-induced reduction of cytoplasmic ca2+ : activation of a ca2+-atpase in the plasma and/or sarcoplasmic reticulum membranes which lowers cytoplasmic [ ca2+ ] in a direct manner or stimulation of ( na+-k+ ) atpase in the cell membrane which may indirectly effect ca2+ extrusion .
C0010834
cytoplasmic
C0007603
cell membrane