Effect of cations on intestinal nutrient transport in two teleosts.

The uptake of sugar and amino acids was affected by the presence of cations in the filling solution in both the fishes, Ophiocephalus and Heteropneustes. Under low Na+ concentration, the rate of transport decreased while an increase in Na+ concentration brought about its corresponding increase in both the fishes. Li+ was able to substitute Na+ to some extent in the filling solution in the transport of xylose, glycine and leucine. The replacement of Na+ by Li+ was more successful in xylose transport, in contrast to the transport of glycine and leucine. On the other hand, K+ was not able to substitute Na+ in the transport process. K+ inhibited the transport of glycine but did not that of xylose and leucine.