Volume regulation in an intertidal oligochaete, Clitellio arenarius (Müller). I. Short‐term effects and the influence of the supra‐ and subesophageal ganglia

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AbstractTerrestrial oligochaetes demonstrate significant volume and osmoregulatory abilities that are under neurosecretory control. In the marine Oligochaete, little is known of volume or osmoregulatory capacities. However, histological evidence has linked cerebral neurosecretion and osmoregulation. The present study investigates water, ion, and volume regulation in an intertidal oligochaete and the effects of ablation of primary neurosecretory centers (supra‐and subesophageal ganglia) on these parameters. Control, sham‐operated, and ablated Clitellio arenarius were acutely transferred to diluted seawaters. Osmolality and Na, K, Cl (mEq/liter) concentrations were determined in total tissue water and in extracellular fluids. Extracellular volume was determined (using micropuncture techniques) as the fraction of the total tissue water in which 14C‐polyethylene glycol was distributed. With transfer to diluted seawater, all worms demonstrated hyperosmotic conformity. Tissue osmolality decreased in all animals at the same rate indicating no effect of ablation on integumental water permeability. Two phases of volume regulation were observed. In phase 1 (0–6 hours) osmolality decreased while water content (gm H2O/gm solute free dry weight = s.f.d.w.) increased both intra‐ and extracellularly. During this period, some volume regulation was accomplished in the control groups, particularly during the first 5 minutes, by the excretion of extracellular Na and Cl (μmoles/gm s.f.d.w.) which limited water gain. Ablated worms, reflecting less extracellular solute loss, gained more water than control groups. In phase 2 (6–18 hours) osmolality was constant, and all groups demonstrated a slow intra‐ (IC) and extracellular (EC) regulatory volume decrease. The solutes that accompanied volume loss were Na (EC), Cl (IC), and unmeasured solutes (IC). Reduction in intracellular solute content was the most significant loss occurring during this period with little difference among the groups tested. We hypothesize the primary effect of ablation is on extra‐ rather than intracellular volume regulation.