Pharmacological properties of curare-sensitive receptors mediating post-tetanic potentiation in rat masseter muscle.

Post-tetanic potentiation (PTP) of single muscle twitches after "tetanic" stimulation at 1 to 20 Hz in rat masseter muscle has been studied. PTP was inhibited by d-tubocurarine (2--6 microgram/kg), hexamethonium (1.75--2.25 mg/kg), succinylcholine (5--7 microgram/kg), prostigmin (1.0--1.5 microgram/kg), lidocain (3--4 mg/kg) and ouabain (215--240 microgram/kg). The doses did not affect the control twitches. Prostigmin could not reverse the blocking effect on the PTP caused by these drugs. Atropin was without any effect on the PTP. The nicotinic receptors mediating PTP differ from both end-plate and ganglionic receptors since drugs blocking both types of receptors are effective. The sensitivity to the blocking agents is higher or the same (in the case of hexamethonium) as for the two other types of nicotinic receptors. Thus the PTP is dependent on activity of a "nicotinic" receptor active during physiological conditions, suggesting the presence of an additional mechanism for neuromuscular transmission in rat twitch fibres.