Cellular neurobiology has been transformed in the past decade by new technologies and fundamental discoveries. One result is an enormous increase in our understanding of how ion channels function in nerve and muscle cells and a widening perspective on the role of ion channels in non-neuronal cell physiology and development. Patch clamp techniques now permit direct observation of the transitions between functional confor- mations of individual ion channels in their native membrane. Recombinant DNA techniques are being used to determine the primary structure of ion channel proteins and to test...