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Ion and water regulation during feeding in the female tick Ornithodorus moubata Kaufman, Susan Elaine


Females of the soft tick Ornithodorus moubata were fed artificially on blood meals of varying ionic and osmotic compositions. Chloride and sodium were actively transported from gut to hemolymph. Potassium ions may have been actively transported from hemolymph to gut or passively distributed across a gut epithelium of low permeability. Water movement across the gut was dependent on the total sodium and chloride transported and on the osmotic pressure difference across the gut wall. Constant sodium chloride concentrations and osmotic pressures were maintained in the hemolymph when ticks were fed meals of differing compositions provided these meals were isosmotic with normal blood. Otherwise the osmotic pressure of the hemolymph paralleled that of the meal. The following evidence led me to conclude that the coxal fluid was produced by ultrafiltration. The coxal gland never produced fluid which was hypertonic to the hemolymph. Inulin showed a coxal fluid: hemolymph ratio of unity over a wide range of inulin concentrations in the hemolymph. Hydrostatic pressure in the hemolymph increased during coxal fluid production and the rate of production was pressure sensitive. The site of ultrafiltration was demonstrated v/hen fluorescein-labelled albumin was trapped in the thin membraneous structure enveloping the tubular part of the gland. The ultra-structure of this membrane was very similar to that of other tissues engaged in filtration. Sodium was actively reabsorbed and chloride moved passively down an electropotential gradient across the resorption tubule of the coxal gland. Potassium was actively transported from hemolymph to resorption cells and passively diffused into the coxal fluid. There was some resorptive capacity for amino acids but they were not regulated to the same degree as inorganic ions. The ultrastructure of the resorption cells was typical of that found in cells engaged in ion and water transport.

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