Influence of atropine on carbachol dual effect on Ca2+ mobilization in SH-SY5Y neuroblastoma cells

The muscarinic receptor stimulated mobilisation of calcium ions in SH-SY5Y neuroblastoma cells was measured as a function on carbachol and atropine co ncentrations. The combined application of this pair of muscarinic agonist a nd antagonist yielded a set of bell-shaped dose-response curves. In the pre sence of atropine the cell responses were smaller and the up-going phase of these relationships was shifted towards higher agonist concentration, whil e the down-going phase of these curves was not influenced by the antagonist . These results pointed to a similar mechanism of the receptor inhibition a t high carbachol (agonist) concentrations and by atropine (antagonist).