Fig. 3. Potassium cyanide significantly reduces Na⁺ uptake by anal papillae of mosquito larvae. Na⁺ concentration gradients at a single point adjacent the surface of isolated (in vitro) anal papillae were measured using the SIET system in a 1 mmol l^–1 Na⁺ bath. After a minimum of 40 min, 30 µmol l^–1 KCN was added to the bath. Results are shown as Na⁺ flux. (A) A representative preparation illustrates the time course of KCN effects on Na⁺ influx. Influx remained consistent for 45 min. KCN was added at the vertical broken line and Na⁺ influx immediately decreased and was abolished in 6 min. (B) Na⁺ influx measured immediately after the preparation was set up (initial), 1 min prior to the addition of KCN (30–45 min) and 5 min after the addition of KCN. Values are mean ± s.e.m. of seven individual papillae. The asterisk denotes a statistically significant difference from the initial measurements.