Seasonal changes in sodium transport and amiloride sensitivity in the isolated intestine of the earthworm, Lumbricus terrestris (L.).

Temporal changes in sodium flux rates and the electrical properties of two regions of the intestine appear to occur in a yearly cycle. In RIIIA, the anterior portion of the mid-intestine, the short-circuit current in January and April preparations is 60.2 and 10.2 microA cm-2, respectively and the net sodium fluxes are 1.50 and 1.24 mu Eq cm-2 hr-1, respectively. In RIIIB, the posterior portion of the mid-intestine, the short-circuit current in January and April preparations is 50.7 and 27.9 microA cm-2, respectively, while the net sodium fluxes are 1.78 and 0.59 mu Eq cm-2 hr-1, respectively. Sodium transport in RIIIB is inhibited by amiloride (10(-4)M) in January preparations but is refractory to amiloride (less than or equal to 10(-3)M) in April preparations.