Haloperidol on rat phrenic hemidiaphragm

The butyrophenone neuroleptic haloperidol (10.65-85.2 microM) blocked the indirectly elicited twitch response of rat phrenic nerve diaphragm preparation. The depression was poorly reversible and was not mediated through dopamine receptors since neither dopamine nor apomorphine could alter the haloperidol blockade. Experiments on the isolated phrenic nerve indicated that the excitability of the nerve was blocked by haloperidol (42.6 microM) and that this blocking effect was minimized in presence of a high concentration of Ca2+ (5 mM) in the bathing fluid. Haloperidol (10.65-85.2 microM) also concentration-dependently inhibited acetylcholine (2.7 microM) contracture, without affecting the potassium chloride (0.5 M) and caffeine (15 mM) contracture. We conclude that haloperidol acts as a local anaesthetic on the motor nerve, probably by affecting calcium channels.