The nature of the interactions of pyridostigmine with the nicotinic acetylcholine receptor-ionic channel complex. II. Patch clamp studies.

Patch clamping of myoballs to record single channels was performed to examine the interaction of the anticholinesterase agent pyridostigmine (Pyr) with the acetylcholine (ACh) receptor-ion channel complex. Single ACh channel currents were recorded from tissue-cultured muscle cells of neonatal rats (myoballs). Pyr (50-100 microM) decreased the frequency of channel-opening events activated by ACh, and induced a modified form of the ACh channel currents. Channel conductance was lower in the presence of Pyr, and channel lifetime remained unaltered or only slightly prolonged. In addition, channel openings were frequently interrupted by fast flickers in the presence of Pyr. Higher concentrations (200 microM-1 mM) of the drug induced irregular waves of bursting activity during the initial phase of the application, and, subsequently, significantly reduced the frequency of channel openings. Infrequent channel openings with low conductance were observed in the patch when the micropipette was filled with Pyr alone. These results suggest that, in addition to its anticholinesterase activity, Pyr reacts with the ACh receptor, and both alone or in combination with ACh induces an altered, desensitized species of the nicotinic receptor-ion channel complex.