Analysis of Epithelial Transport by Measurement of K+, Cl− and pH Gradients in Extracellular Unstirred Layers: Ion Secretion and Reabsorption by Malpighian Tubules of Rhodnius Prolixus

Summary The pH and concentrations of K+ and Cl- in the unstirred layer (USL) associated with the basolateral surfaces of the upper and lower Malpighian tubules of Rhodnius prolixus were measured using extracellular ion-selective microelectrodes. When stimulated with 5-hydroxytryptamine (5-HT) in vitro, the upper Malpighian tubule secretes Na+, K+, Cl- and water at high rates; the lower Malpighian tubule reabsorbs K+ and Cl- but not water. …