The effect of imipramine on isolated skeletal muscle preparations.

Imipramine (2-10 microng/ml) noncompetitively inhibited acetylcholine responses of the frog rectus abdominis muscle, and markedly inhibited the contracture produced by carbachol and succinylcholine without affecting the contracture produced by KCl, caffeine, and chlorpromazine. The twitch responses to indirect and direct stimulation of the rat phrenic nerve-diaphragm and the frog sciatic nerve-gastrocnemius were first augmented and then depressed markedly and irreversibly by imipramine (5-20 microng/ml). The indirect stimulation was inhibited earlier and to a greater degree than the direct stimulation. The blockade in the nerve-sartorius developed and progressed quickly without prior augmented responses, and with a parallel time course for indirect and direct stimulation. On the frog rectus, physostigmine antagonised whereas d-tubocurarine and CaCl2 increased the imipramine-induced inhibition. In the nerve muscle preparations, physostigmine, CaCl2 and KCl did not affect the neuromuscular blockade produced by imipramine; tubocurarine (0.05 microng/ml) markedly increased the blocking effect of imipramine (20 microng/ml) on the rat phrenic nerve-diaphragm. The results have been discussed in relation to the memberane stabilizing and the calcium releasing actions of imipramine.

Isolated innervated, rat and guinea-pig hemi-urinary bladder preparations.

Isolated innervated hemi-urinary bladder preparations of the rat and the guinea-pig have been described. In durability and behaviour to different frequencies of stimulation, the guinea-pig hemi-bladder is shown to give comparable results to those reported for the whole nerve-bladder. The rat hemi-bladder gave less durable contractions on prolonged stimulation. It is shown that the isolated guinea-pig hemi-bladder can be substituted for the isolated whole bladder preparation.