[Atypical endplate miniature potentials in the frog neuromuscular junction after modification of the intercellular matrix and osmotic exposures].

In frog cutaneous-pectoris muscles the frequency of slowly rising atypical miniature endplate potentials (MEPPs) was significantly enhanced after collagenase (0.1%) treatment. Treatment with trypsin, hyaluronidase, hyper- and hypoosmotic solutions caused no changes in slowly rising MEPP (frequency in muscle fibers with intact acetylcholinesterase (AChE). Inhibition of AChE caused appearance of giant MEPPs. Acceleration of acetylcholine diffusion from synaptic cleft after treatment with hyaluronidase decreased giant MEPP frequency demonstrating their dependence upon nonhydrolyzed acetylcholine in synaptic cleft. The relation between slowly rising MEPPs and activity of synaptic Schwann cells in discussed.