Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 7

Mind the Gap. Gap junctional communication can be examined using a variety of experimental tools. One of these is known as dye coupling, the ability of small fluorescent molecules to pass from one cell to another through gap junctions, a technique pioneered by Werner Loewenstein and his colleagues. What can you conclude about gap junctions from each of the following experiments
(a)Loewenstein and colleagues injected cells with fluorescent molecules of different molecular weights, and a fluorescence microscope was then used to observe the movement of the molecules into adjacent cells. When molecules with molecular weight of 1926 were injected, they did not pass from cell to cell, but molecules with molecular weight of 1158 did.
(b)Microglia (support cells in the brain)are connected by gap junctions. When the fluorescent dye Lucifer yellow is injected into individual microglia that are part of a large group of cells, little dye passes to other cells. When microglia are treated with the calcium ionophore, 4Br-A23187, there is a dramatic increase in dye passage between cells.