Cell volume maintenance and volume regulatory decrease in malpighian tubule cells of an inspect, Rhodnius prolixus

1.1. Cell volumes of the upper portion of the lower segment of Malpighian tubules were calculated from optical measurements of tubular dimensions in isosmotic and hyposmotic salines.2.2. Cell volume maintenance in isosmotic saline requires sodium; cells swell when sodium is replaced by potassium or choline.3.3. When isosmotic bathing saline is replaced by hyposmotic saline, cells swell initialy, but cell volume is subsequently reduced, toward the isosmotic volume. Regulation was inhibited by low temperatures, dinitrophenol, preincubation in ouabain, or elevated potassium concentrations.4.4. The results suggest that leakage of K+, an accompanying anion, and osmotically-obliged water contribute to volume regulation in hyposmotic salines.