Fig. 4. Effect of cadmium alone and cadmium + Na⁺/H⁺ exchanger inhibitors on PK activity of isolated digestive gland cells of Mytilus galloprovincialis. 100% represents enzyme activity in the absence of cadmium (5.23±1.04 nmol min^–1 mg^–1 protein). Cells were treated for 30 min either with 50 µmol l^–1 of cadmium alone, or 50 µmol l^–1 cadmium + 10 µmol l^–1 amiloride (an inhibitor of most plasma membrane Na⁺ transport systems) or + 20 nmol l^–1 EIPA (a selective inhibitor of Na⁺/H⁺ exchanger). PK activity in the presence of 20 nmol l^–1 EIPA alone after 30 min of incubation was found to be 5.38±0.7 nmol min^–1 mg^–1 protein. The results (expressed as % PK activity of control value) are mean ± S.D. of at least 7 independent experiments. In each experiment, the tissue from four animals was used. ^*Significant difference between the value after cadmium treatment and the control value; significant difference between the values after cadmium treatment with those observed after cadmium + inhibitors; Dunnet's test, P<0.01.