The effects and interactions of caffeine, lignocaine and carbachol at the chick neuromuscular junction.

The effects and interactions of lignocaine, carbachol and caffeine on the contractile response and endplate potential were investigated in the isolated chick biventer cervicis nerve-muscle preparation using a moving fluid electrode technique. Lignocaine (37 microM-1.8 mM) produced a dose-dependent contracture response that was not related to an endplate depolarization and appeared to inhibit non-competitively the usual depolarization and contractile response to carbachol (5.5 microM-0.8 mM). In contrast, lignocaine enhanced the contractile response to caffeine (0.54-10.8 mM) possibly by lowering the threshold and mainly by increasing the maximal response. The peak effects occurred at the same caffeine concentration regardless of the presence of lignocaine. The possibility that both lignocaine and caffeine may produce contractures in the chick muscle by acting on intracellular calcium concentration is discussed.