Genetic dissection of Ca2+‐dependent ion channel function in Paramecium

The ciliated protozoan, Paramecium, broadcasts the activity of its individual ion channel classes through its swimming behaviour. This fact has made it possible to isolate mutants with defective ion currents, simply by selecting individuals with abnormal swimming patterns. At least four of Paramecium's ion currents are activated by rising intracellular calcium concentration, including two K+ currents and a Na+ current. A variety of cell lines with defects in these Ca2+-dependent currents have been isolated: in several cases, the defects have been traced to mutations in the structural gene for calmodulin. Sequence analysis of calmodulins from these and other Ca2+ -dependent ion-current mutants may enable a detailed mapping of putative channel interaction domains on the surface of the calmodulin molecule.