Functional states and fine structure of the contractile apparatus of the penis retractor muscle (PRM) of Helix pomatia L.

The ultrastructure of the isolated glycerinated penis retractor muscle (PRM) of Helix pomatia was investigated. The diameter distributions of thick myofilaments from birbre cross sections in the relaxed, phasic contracted, tonic contracted, and in the catch state.s show that a characteristic filament spectrum is formed in the catch state and its preceding active state. The significant structural differences are discussed in relation to earlier hypotheses related to the catch state