Sodium ion uptake by perfused gills of the blue crab Callinectes Sapidus; effects of ouabain and amiloride

Abstract

ABSTRACT Sodium ion uptake in the isolated perfused posterior gill of the blue crab, Callinectes sapidus Rathbun, acclimated to 5‰ salinity and 20°C was measured using 22Na as a tracer. Unidirectional influxes across individual gills occurred against large sodium concentration differences (internal perfusate=273 mmol l−1; external perfusate=l–80 mmol l−1) and depended strongly on the concentration of sodium ions present in the external perfusate. The maximum rate of influx was 3.24 μmol g−1 min−1 and the Km for this process was 23.0 mmol l−1. Ouabain added to the internal perfusate reduced the influx to an average of 51.3 % of the control values and had its maximal effect at 1 mmol l−1. Ouabain (1 mmol l−1) added to the external perfusate had no significant effect on sodium influx. Amiloride (0.1 mmol l−1) added to the external perfusate reduced the influx to an average of 38.9 % of the control values. During all treatments, perfusion pressures showed no treatment-dependent effects, indicating that the observed changes in fluxes were due to specific effects of the treatment on the epithelium and not due to some indirect effect on perfusion pattern within the gill. Treatment of the gill with the metabolic poisons cyanide and iodoacetate resulted in a rapid decline of sodium influx to 20–30% of the control values. This was correlated with a large reduction in gill ATP content to 13% of the control. The overall results of this study are consistent with the general picture of epithelial sodium uptake across gills, supporting the existence of a ouabain-sensitive Na+ pump on the basolateral membrane and an amiloride-sensitive Na+/H+ exchanger on the apical membrane.