Dear Jean,

ACh is usually quite stable in stock solutions of aliquots in freezer, and I usually prepare daily fresh solutions from frozen stocks. I apply it on to isolated cells in culture dish and have no problem with responses.  I think if you are not seeing and responses it is more likely due to your application method. Especially if you are working with whole muscle mass it can be a bit hard to get ACh into the right spot at the right concentration, as the muscle fascia and connective tissue may be preventing the access of ACh into the tissue at the high enough concentration to evoke contraction. Another alternative could be to try nicotine instead of ACh.

best wishes, Refik

The usual solution in vertebrates is carbamylcholine chloride (carbachol). It stimulates both muscarinic and nicotinic receptors and is quite stable. I don't know about its pharmacology in mussels.

Ach is insanely hygroscopic. It will absorb water in a vacuum dessicator over dessicant and becomes a sort of wet lump.