Sodium transport in erythrocytes of the mollusc Anadara broughtonii: Evidence for inhibition by quinine

Abstract

Sodium transport through the molluscan erythrocyte membrane was examined using 22Na as a tracer. Incubation of the red cells in standard saline resulted in a rapid 22Na uptake reaching steady state concentration (about 21.5 mmol/l cells) in the first 60 min. A similar pattern in the time course of 22Na uptake was seen in the erythrocytes incubated in mantle fluid. The average value of unidirectional Na + influx, measured as a 5-min 22Na uptake, was 7.76 ± 0.36 mmol/1 cells/5 min or 93 ± 4.3 mmol/1 cells/hr. The initial rate of Na + influx increased in a saturable fashion as a function of external Na + concentration with apparent AT., of 380±12mM and V max of 14.3 ± 2.4 mmol/1 cells/5 min. Amiloride (1 mM), furosemide (1 mM), and DIDS (0.1 mM) had no effect on either initial Na + influx (5 min 22Na uptake) or equilibrium Na + concentration (60 min and 120min 22Na uptake) in the molluscan red cells exposed to standard saline. Quinine (1 mM) caused a significant fall in the initial Na + influx (by 48%) and in 60-min 22Na uptake (by 32%) as compared with control levels. In the presence of 0.1 mM ouabain, 22Na uptake into the red cells was enhanced by an average 27% and 44% during 60 min and 120 min of cell incubation, respectively. The ouabain-sensitive Na + accumulation in the red cells reflected a contribution of the Na, K-pump to Na + transport and the mean value was 5.6 ± 1.0 mmol/1 cells/hr.