An X-ray microanalysis study of Locusta Malpighian tubule cell function using rubidium.

Intracellular distributions of Na, K, Mg, Ca, Cl, P, and S were determined in type 1 Malpighian tubule cells of Locusta using X-ray microanalysis. K showed a gradient of increasing concentration from basal to apical surfaces. No other element showed this distribution. Na was below the detection limit. Three types of dark body were present in cytoplasm; one rich in Ca and P and two rich in K and P. Incubation in Rb-Ringer solution resulted in a dramatic fall in cellular K that was not completely replaced by Rb. The distribution of Rb mimicked that of K. Na levels were significantly increased, but the total intracellular monovalent metal concentration was less than in controls. Other elements were little affected. Rb replaced K in dark bodies. Tubules continued to secrete K-rich urine in Rb-Ringer solution even though intracellular [K] was low. Little Rb+ was secreted and Na+ secretion was unchanged. The possible role of dark bodies as a source of secreted K+ is discussed.