Sucrose gap

The sucrose gap technique is used to create a conduction block in nerve or muscle fibers. A high concentration of sucrose is applied to the extracellular space, which prevents the correct opening and closing of sodium and potassium channels, increasing resistance between two groups of cells. It was originally developed by Robert Stämpfli for recording action potentials in nerve fibers, and is particularly useful for measuring irreversible or highly variable pharmacological modifications of channel properties since untreated regions of membrane can be pulled into the node between the sucrose regions.

The sucrose gap technique was first introduced by Robert Stämpfli in 1954 who worked with Alan Hodgkin and Andrew Huxley between 1947 and 1949. From his research, Stämpfli determined that currents moving along nerve fibers can be measured more easily when there is a gap of high resistance that reduces the amount of conducting medium outside of the cell. Stämpfli observed many problems with the ways that were being used to measure membrane potential at the time. He experimented with a new method that he called the sucrose gap. The method was used to study action potentials in nerve fibers.

Huxley observed Stämpfli’s method and agreed that it was useful and produced very few errors. The sucrose gap technique also contributed to Stämpfli's and Huxley's discovery of inhibitory junction potentials. Since its introduction, many improvements and alterations have been made to the technique. One modification of the single sucrose gap method was introduced by C.H.V. Hoyle in 1987. The double sucrose gap technique, which was first used by Rougier, Vassort, and Stämpfli to study cardiac cells in 1968, was improved by C. Leoty and J. Alix who introduced an improved chamber for the double sucrose gap with voltage clamp technique which eliminated external resistance from the node.

A classic sucrose gap technique is typically set up with three chambers that each contain a segment of the neuron or cells that are being studied. The test chamber contains a physiological solution, such as Krebs or Ringer's solution, which mimics the ion concentration and osmotic pressure of the cell's natural environment. Test drugs can also be added to this chamber to study the effect that they have on cellular function. Ag-AgCl or platinum wire electrodes are generally used for stimulating the cells in the test solution. The sucrose chamber (or gap) is the middle chamber that separates the two other chambers, or sections of the nerve fiber or cells. This chamber contains an isotonic sucrose solution of a high specific resistance. Specific resistance describes the ability of a material or solution to oppose electric current, so a sucrose solution of a high specific resistance is effective in electrically isolating the three chambers. The third chamber usually contains a KCl solution that mimics the intracellular solution. The high potassium concentration in this chamber depolarizes the immersed segment of the tissue, allowing potential differences to be measured between the two segments separated by the sucrose gap. Vaseline, silicon grease, or a silicon-vaseline mixture is used to seal the nerve or tissue in position and prevent diffusion of solution between the chambers. A pair of agar-bridged Ag-AgCl electrodes are placed in the test and KCl chambers to record the changes in membrane potential.

...
Wikipedia