A threadlike structure in the abdominal cavity closely resembled the primo vascular system (Bonghan system), which was proposed to be the anatomical reality of acupuncture meridians. The threadlike structure consisted of thread parts and nodes. The membrane potential of cells from the thread parts and the nodes was measured to investigate the electrophysiological characteristics of the cells and to verify the existence of excitable cells. To this end, an intracellular recording technique was applied to measure the action potentials. We examined approximately one hundred threadlike structures in order to measure the spontaneous action potentials. Interestingly, we succeeded in three cases, two of which were from thread parts and one from a node. Moreover, the shapes of the action potentials were very unique. Although the shapes of these three cases differed from one another, the full widths at half maximum (FWHMs) of the action potentials were tens of milliseconds for all three. The FWHMs were significantly different from those of a neuron, a skeletal muscle cell, and a cardiac muscle cell. This result suggests that these action potentials were measured from smooth muscle cells, secreting cells, or immune cells.