Identification of the two cell groups in the longitudinal muscle layer of the earthworm Amynthas hawayanus by a single microelectrode with lucifer yellow-CH.

Previous electrophysiological studies have suggested the presence of two types of muscular cells in the longitudinal muscle of A. hawayanus. However, a definite classification of such cells as muscles has been hindered by lack of morphological evidence. This study identified these cells electrophysiologically and morphologically by using the same intracellular microelectrode to record cell activity and inject Lucifer Yellow-CH. Electrophysiological measurements clearly differentiated the two groups of cells. One group did not respond to nerve stimulation but was spontaneously active, whereas the other responded to nerve stimulation with endplate potentials and did not discharge spontaneously. Morphological examination revealed two very similar types of longitudinal muscle cells. These results clearly show that, although morphologically similar, there are two distinct groups of muscle cells in the longitudinal muscle layer of the earthworm.