Zonation of Ca2+ transport and enzyme activity in the caeca of rainbow trout - a simple structure with complex functions [RESEARCH ARTICLE]

Melanie Williams, Domenico Barranca, and Carol Bucking Trout caeca are vermiform structures projecting from the anterior intestine of the gastrointestinal tract. Despite their simple gross morphology, these appendages are physically distinct along the anterior-posterior axis and ultrastructural evidence suggests zonation of function within the structures. Individual caeca from three sections (anterior, middle, posterior) were removed from the intestine of freshwater rainbow trout and investigated for ion transport and enzyme activity. Ca2+ absorption appeared as a combination of active and passive movement, with Michaelis-Menten kinetics observable under symmetrical conditions, and was inhibited by several pharmacological agents (ouabain, La3+, and a calmodulin antagonist). There was a decrease in ion transport function from adjacent to the intestine (proximal) to the distal tip of each caeca, along with decreasing transport from anterior to posterior for the proximal portion alone. Feeding increased the JMax and KM for Ca2+ absorption within all sections, while Ion-Poor Water (IPW) exposure further increased the JMax and KM for Ca2+ transport in the anterior and middle sections alone. Increased Na+-K+-ATPase (NKA) and Citrate Synthase (CS) activity rates paralleled trends seen in Ca2+ transport. Feeding in freshwater and IPW exposure increased the glycolytic capacity of the caeca via increased Pyruvate Kinase (PK) and decreased Lactate Dehydrogenase (LDH) activity, while ami...
Source: Journal of Experimental Biology - Category: Biology Authors: Tags: RESEARCH ARTICLE Source Type: research