 Dear students, In this topic, we shall discuss the localization and characterization of ion channels. Dear students, in the 1940s and 50s, two scientists Hodgkin and Huxley performed a large number of experiments using the joint axones of squids. They found that during action potentials, the conductance of membrane for sodium and potassium ions changes. At that time, the ion channels had not been discovered. So due to their experiments, Hodgkin and Huxley predicted that there should be some ion channels present in the membrane that control the conductance of sodium and potassium ions. After Hodgkin and Huxley, many technical advances took place that contributed to the understanding of nature of these ion channels. The major development was the development of technique for measuring ionic grunts across the membrane. The technique that was developed is known as patch clamp technique. Similarly, the techniques for the study of protein chemistry and molecular biology helped to identify the channel proteins. As a result of all these developments, now the molecular protein nature of ion channels was established. In localizing the ion channels in the membrane, there has been a great role of neurotoxins. The neurotoxins have the capacity to bind to specific ion channels and block them. That is also the basis of their toxicity and that character was used to localize ion channels in the membrane. An important neurotoxin is the TTX or Tetrodotoxin. This toxin is obtained from Japanese puffer fish. It selectively blocks the fast-acting sodium voltage-gated sodium channels. Radioactively labelled, TTX is used to estimate the density of sodium channels in the membrane. Now it is, new techniques have developed for the localization and characterization of these ion channels. One of these is the use of antibodies. Antibodies can be developed for specific ion channels. They bind with specific channels and the antibody labelled channels can be viewed directly under the microscope.