Electrophysiology of the Somatic Muscles in the Nematode Ascaris lumbricoides

Abstract

The electrical activity of the somatic muscles of the parasitic nematode Ascaris lumbricoides has been investigated. The functional muscle syncytium overlying the nerve cord is preferentially excited by anodal stimulation with an extracellular electrode. Cathodal stimulation preferentially excites the nerve cord, allowing determination of separate conduction velocities for the nerve cord and syncytium. The propagation velocity of the nerve cord is 16.2 ± 1.2 cm/sec; that of the syncytium varies with the calcium concentration, being 21.6 ± 1.3 cm/sec for unitary slow waves under normal conditions. Both values are too high to account for the propagation of contractile waves in the intact animal. Ascaris muscle gives rise to complex spontaneous depolarizations consisting of slow waves and graded spike potentials. Often, the spikes and slow waves are modulated into periodic bursts of electrical activity, which gives rise to rhythmic contractions on a behaviorally significant time scale. Spikes appear to be mediated exclusively by calcium ions the spike active potential varies with calcium concentration as expected for a calcium electrode and spikes persist in sodium-free media. Slow waves can be mediated by either sodium or calcium ions; they persist when calcium or sodium are removed separately, but not when both are removed together. In rhythmically active preparations, a burst of slow waves and spikes accompanies each contraction. The modulation shows dorsal-ventral coordination if the right lateral line is intact, in accord with known nervous system asymmetry. Anterior-posterior coordination is also observed.