Effects of Intraluminal Pressure on Motility in the Crop and Gizzard of the Earthworm, Lumbricus terrestris

Abstract

The present study was designed to examine motility in the isolated earthworm gut. The physiological significance of, environmental stimuli that trigger, and cellular and molecular basis of gut motility in this species are unclear. Earthworms (Canadian Nightcrawlers) were obtained from a local fishing bait supplier. Worms were kept at 4 °C until the day of study. Worms were housed in worm bedding until 2–7 days prior to experimentation, at which time they were transferred into a petri dish lined with a water‐moistened paper towel to allow the gut to be partially emptied. On the day of study, worms were anesthetized by placing them in a beaker containing 200 ml of tap water and 1–2 Alka‐Seltzer tablets. Anesthetized worms were dissected, and the crop and gizzard was removed en bloc, cleaned of adhering septal and connective tissue, and transferred to a tissue bath containing worm saline at room temperature (~20 °C). The gut preparation was cannulated at both ends using 20G stainless steel hypodermic tubing. The lumen was filled with worm saline. The distal cannula was connected to a pressure transducer and closed by a stopcock. The proximal cannula was connected to a 30 ml syringe filled with worm saline that was open to atmospheric pressure. The height of the syringe could be raised and lowered to control intraluminal pressure. The preparation was equilibrated at ambient pressure for approximately 30 minutes. Following equilibration, intraluminal pressure was elevated incrementally every 5–10 minutes. A camera placed above the tissue bath recorded video (30 frames per second) during each pressure maneuver. The video was analyzed off line using a custom spatiotemporal mapping algorithm to assess luminal diameter. We found that the gut exhibited very low amplitude (<1 mmHg) pressure fluctuations at ambient pressure, and these pressure fluctuations were associated with waves of constriction/dilation in the gut lumen. Raising intraluminal pressure slightly from 0 to 2 mmHg induced a robust motor response such that the organ first passively dilated in response to the increase in intraluminal pressure, and then both gut regions constricted by up to 30%. The constrictions were followed by dilations, and this pattern continued, such that motility appeared as phasic waves of constriction/dilation. These robust phasic motor patterns were associated with large amplitude (20 mmHg) pressure pulsations. Larger motor events were in phase with larger pressure pulsations, and smaller motor events occurred in phase with smaller pressure pulsations. At higher intraluminal pressures (10 mmHg), the gut passively dilated, and motor events ceased, while intraluminal pressure passively tracked the applied hydrostatic pressure with no further pressure pulsations. Thus, we conclude that the earthworm crop/gizzard exhibits a robust mechanical response that is triggered by distention of the organ wall occurring with elevated intraluminal pressure. This response is likely to be of physiological significance, and may underlie peristalsis and propulsion of luminal contents in this species. The cellular and chemical basis of this response is not known.Support or Funding InformationSupport provided by Med Associates and Catamount Research and Development.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.