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Mechanism of water and salt absorption in the in vitro locust rectum Goh , Soon Leong

Abstract

A method is described for the preparation of an everted rectal sac of the desert locust. Water and solute absorption by the rectum was determined by measuring changes in hemocoel fluid and rectal tissue. Initial absorption rates of Na, K, Cl, water and trans-rectal potential are comparable to those in vivo under similar conditions. After an initial transient period (1 hour), transport activity of the in vitro rectum remained in a steady state for at least 4- hours. The relationship between osmotic gradient and steady state rate of net water movement across the rectal wall was determined. Absorption of water is partially inhibited by anoxia, malonate (10־² M), dinitrophenol (10־³M), potassium cyanide (10־³ M) plus iodoacetate (10־³ M) and ouabain (10־³ M). Tissue ions and water are secreted into the hemocoel compartment when the rectal sac is incubated in isosmotic pure sucrose solution. Dependence of water movement on solute transport is indicated by the requirement of lumen ions for prolonged maintenance of water absorption. Effects of different ions (Na, K and Cl) in bathing media on absorption rate of water and ions, absorbate concentrations, trans-epithelial electro-potential differences, and tissue compositions were determined. Observed properties of water and solute movement in vitro are discussed and evaluated in relation to possible mechanisms for active absorption of water. Possible locations of transport sites are suggested in a hypothetical scheme based on the ultrastructure of rectal epithelium.

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