Fig. 5. Assessment of HCO₃^– dependency for Na⁺ uptake by bled and un-bled L. stagnalis as tested under control (sodium bicarbonate) and treatment (NaCl, sodium gluconate or sodium sulfate) conditions. Each treatment medium contained 500 µmol l^–1 of Na⁺. Differences between un-bled and bled conditions within treatments were significantly different. There were no significant differences among sodium treatment groups in un-bled or bled conditions. N=10 in all cases except control (NaCl, N=8) and sodium gluconate treatment (N=9). Values are means ± s.e.m.