Oxotremorine neuromuscular blockade: effects of calcium and neostigmine and interactions with D-tubocurarine and decamethonium.

The neuromuscular blocking effect of oxotremorine (OT) on the indirectly stimulated rat diaphragm preparation was compared with that of d-tubocurarine (TC) and decamethonium (C10). Approximate equieffective concentrations of these compounds were 20 micrometer for OT, 1.8 micrometer for TC, and 75 micrometer for C10. Increasing the Ca2+ concentration by 1 mM reduced the rate of onset of OT and C10 blockades whereas TC blockade was almost completely reversed. Neostigmine (NEO) antagonized TC blockade while OT and C10 blockades were enhanced. A facilitatory after-effect of NEO was suppressed in preparations previously exposed to OT but not in those previously exposed to TC or C10. C10 transitorily antagonized TC blockade but not OT blockade. OT did not antagonize TC blockade. A subreceptor effect may be involved in the action of OT and may explain its differences when compared to C10.