The protozoan, Paramecium tetraurelia undergoes a behavioral response in the form of backward swimming to a variety of stimuli. Backward swimming is correlated with action potentials that can be recorded across the surface membrane of the organism. The action potential involves four specific ion channels, a voltage-dependent calcium channel, a voltage- dependent potassium channel, and two calcium dependent channels, one that is selective for potassium and the other for sodium. The overall goal of this research is to understand the molecular components involved in the regulation of the calcium-dependent potassium channel from Paramecium. Recent studies using the behavioral mutant called pantophobiac have shown that the calcium-binding protein, calmodulin, is involved in the regulation of the calcium-dependent potassium channel. To understand more fully the molecular mechanism of the regulation of this channel and the role of the channel in the behavior of Paramecium a combined genetic and biochemical approach will be taken. Biochemical changes in pantophobiac mutants that affect the channel will be characterized more fully, and calmodulin-binding proteins involved in channel regulation will be isolated and characterized. Ion channels in cells are generally composed of complexes of membrane proteins, and function as gated pores for the orderly transport of ions across cell membranes. Their function, besides being involved in the behavior of Paramecium, is the basis for excitation in nerve and muscle and for the responses of many cell types to environmental stimuli. The molecular mechanisms by which ion channels function are, as yet, poorly understood. Paramecium provides an excellent system for basic studies of ion channels because it can be genetically manipulated and large numbers ofidentical cells can be obtained to provide sufficient material for biochemical studies. The results of this research will provide important new information about the molecular mechanism of regulation of the calcium-dependent potassium channel.
