Renal function in sea snakes: II. Sodium, potassium, and magnesium excretion

Renal clearance studies performed on the sea snake Aipysurus laevis demonstrated net tubular reabsorption of Na and both net tubular secretion and reabsorption of Mg and K. Fractional excretion of Na (FE(Na)) was 0.05 under control conditions and increased markedly with hyperosmotic salt loading. Within each group, however, higher glomerular filtration rates were accompanied by disproportionately greater Na reabsorption. FE(Mg) was 0.66 under control conditions and increased with Mg loading. The rate of Mg secretion was positively correlated with the urine flow rate. However, Mg loading caused a flow-independent increase in Mg secretion that was correlated with increasing plasma Mg concentration. FE(K) was 0.86 under control conditions and increased with K loading as a result of enhanced K secretion by the renal tubules. Like renal Mg secretion, renal K secretion showed a flow-dependent component as well as a flow-independent component related to plasma K concentration.