Genetic dissection of the excitable membrane of Paramecium

Paramecium aurelia is chosen as the material for a genetic dissection of the excitable membrane. The simple innate behavior makes the behavioral analyses easy and mutant screening possible. Autogamy, which leads to complete homozygosity, guarantees the expression of recessive mutations. The size of these giant cells allows intracellular recording in electrophysiological studies.--Some two hundred lines of behavioral mutants are isolated. Several of them are studied in detail genetically, behaviorally as well as electrophysiologically. Mutants devoid of proper active electrogenesis are now available. Some of them are shown to be temperature-dependent. They have a slightly aberrant electric pattern when grown at the permissive temperatures and lose their excitability completely when cultured at the restrictive temperatures.--Systematic modifications of the membrane excitation process is demonstrated in this interdisciplinary study. Three unlinked mutations are shown to block the generation of Na-triggered depolarizations at different positions resulting in three different altered forms of electrical activities. The bioelectric profiles of 25 types of single or double mutants are now known. The search for the relevant gene products on the surface membrane is now underway.