Active Transport in Insect Malpighian Tubules

Abstract:: The Malpighian tubules of insects are an excellent model for examining the properties of secretion in a transporting epithelium. In this exercise students expose tubules from cockroaches or crickets to chlorophenol red and visually estimate the dye concentration in the lumen. By adding metabolic inhibitors and competitors or by substituting ion-free media they can demonstrate competition, specificity, and energy- or ion-dependence of active transport. Advanced students can design their own experiments after a review of the literature. This simple and inexpensive exercise provides students with a challenging and rewarding introduction to experimental design in the laboratory.

Quantitative Physiology: Cells and Tissues, Fall 2004

Abstract:: Principles of mass transport and electrical signal generation for biological membranes, cells, and tissues. Mass transport through membranes: diffusion, osmosis, chemically mediated, and active transport. Electric properties of cells: ion transport; equilibrium, resting, and action potentials. Kinetic and molecular properties of single voltage-gated ion channels. Laboratory and computer exercises illustrate the concepts. For juniors and seniors. Students engage in extensive written and oral communication exercises.

Read the Fine Print

Abstract:: Readily available from suppliers, this larva has a large midgut that specializes in transporting excess potassium (from its plant food) into its lumen. The exercise is offered as an alternative to the traditional study of frog skin. In this exercise, the midgut is mounted on a perfusion tube, and the electrical potential difference across the wall of the midgut is measured with an oscilloscope which provides data on the rate of potassium transport. The basic set-up is amenable to the study of a variety of interesting questions.