Investigation of the mode of action of the anaesthetic agent, ketamine, in the heart of the bivalve mollusc Tapes watlingi.

In the isolated heart preparation from the bivalve mollusc Tapes watlingi the anaesthetic agent ketamine produced two distinct effects; a positive inotropic effect and bradycardia. The dose-dependent positive inotropic effect was considered to be a direct effect on the cardiac muscle since it was not blocked by antagonists specific for the excitatory actions of acetylcholine, dopamine, serotonin and octopamine. Verapamil, a calcium ion antagonist, did not affect the inotropic response. The bradycardia caused by ketamine was blocked by inhibitors specific for the acetylcholine receptor but not by specific antagonists to the inhibitory dopamine receptor.