Analysis of the distribution of sodium, potassium and osmotic pressure in the urine of crayfishes.

Studies of ion concentrations and osmotic pressures in the crayfish antennal gland have revealed a major discrepancy. The osmotic pressure of the urine in the tubular portion of the gland falls (Riegel, 1963). However, the sodium and potassium concentrations measured there exceed the osmotic pressure (Riegel, 1965). To complicate the situation further, studies of inulin excretion indicate that water absorption occurs in the distal tubule. Further, amino acids become concentrated in the distal tubule (Riegel, 19666). There are two apparent explanations for this discrepancy: one, the original osmotic pressure measurements were in error. Two, a major portion of the particles in the distal tubule are present in an osmotically inactive form. During investigations of the latter possibility it was discovered that formed bodies are found in all parts of the antennal gland (Riegel, 1966a, b). It is possible that the formed bodies represent a site of localization of osmotically active particles. Therefore studies were made of the possible association of sodium and potassium with the urinary formed bodies. The results of these and other studies related to the problem are presented here.