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The function of the anal papillae of saline-water mosquito larvae

University of British Columbia

The role of the anal papillae of saline-water mosquito larvae is uncertain. Sodium ion and Cl¯ uptake by the papillae of larvae in dilute media has been demonstrated (Phillips and Meredith, 1969a). Indirect ultrastructural and physiological evidence suggests that these organs might also be active in ion transport under saline conditions (Phillips and r Meredith, 1969a; Meredith and Phillips 1973a, b; Bradley and Phillips, 1975; Phillips and Bradley, 1977; Phil 1 ips et al., 1 977) . Two possible functions of the anal papillae in saline media have been suggested: (1) that the papillae excrete Na+ and Cl⁻, and (2) that the papillae take up ions present in low concentration in saline waters. Uptake of K⁺ by the anal papillae was measured for the investigation of the second hypothesis. Completion of this study involved measuring the total K⁺ balance of the larvae. These hypotheses were tested by measuring hemolymph osmolarity and ion concentrations of normal and papillaeless larvae in a range of salinities, measuring ⁴²K influx, total body K⁺ content, and the electro-potential difference across the papillae. The anal papilae of the saline mosquito larva, Aedes taeniorhynchus, living in saline waters did not actively take up K+. Indirect evidence indicated that the anal papillae were also not involved in Na+ or Cl⁻ secretion in concentrated media. When A. taeniorhynchus larvae were reared in distilled water, the anal papillae were responsible for nearly all the K⁺ uptake, as is the case for strictly freshwater species of mosquito larvae. The observed influx of K⁺ across the papillae of 46 nmol cm⁻² h⁻¹ occurred against both chemical and electrical potential gradients, indicating that transport is active. Potassium uptake by the anal papillae was also observed in the saline mosquito larva, Aedes campes tri s, from both dilute (about 10 m0sm) and concentrated (about 300 m0sm) solutions although uptake was much reduced in the latter. Uptake was increased by acclimation of the larvae to dilute media. Potassium influx occurred against the concentration gradient but along the electrical p o -. tential gradient. Uptake followed Michaelis-Menten kinetics with an approximate K0.5 of 3.2 mM and Vmax of 1.1 nmo1 mg⁻¹ h⁻¹.

Text

2010-02-21

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http://hdl.handle.net/2429/20658

Zoology

University of British Columbia

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