The long-term goal of this project is to determine the mechanisms by which cells control the ionic currents of their membranes. Two approaches are being used: the first approach focuses on the changes in membrane properties that can be induced by changes in the environment of the membrane. These studies use the neuronal cell bodies of snails (Limnea, Helix, Helisoma), on which sophisticated electrophysiological studies are possible. An internal-perfusion, voltage-clamp technique has been developed which allows the effects of interacellular, as well as extracellular, ions and molecules on membrane currents to be measured. Studies will be made of the dependence of Ca currents on intracellular molecules normally depleted by perfusion, the modulation of voltage-dependent currents by external application of neurotransmitters, the relation between membrane properties and cell function, the alteration of membrane currents by maintenance in vitro, and the effects of growth temperature on membrane properties. The second approach examines the changes in membrane properties that can be produced by point mutations in the genome. These studies will be done on the muscle cells of the nematode Caenorhabditis elegans, or neuronal cell bodies of the fruit fly Drosophila; both animals are convenient for genetic studies. The internal-perfusion, voltage-clamp technique has proven applicable to cells as small as these. The membrane currents of the wild-type animals will be determined, and then cells from a number of behavioral mutants will be examined for alterations in membrane properties. Due to the importance of interacellular Ca++ in controlling muscle contraction, transmitter release, and other cellular functions, primary attention will be given in all of the above studies to effects on the Ca current and overlapping K currents, which determine the influx of Ca++ into the cell. Mechanisms discovered or elucidated by this project will contribute significantly to the understanding of neural and muscular diseases that involve altered states of membrane excitability or synaptic efficacy.