Restoration by calmodulin of a Ca²⁺-Dependent K⁺ current missing in a mutant of paramecium

A combination of genetics, biochemistry, and biophysics was used to show that calmodulin is involved in the regulation of an ion channel. Calmodulin restored the Ca²⁺-dependent K⁺ current in pantophobiac, a mutant in Paramecium that lacks this current. The restoration of the current occurred within 2 hours after the injection of 1 picogram of wild-type calmodulin into the mutant. The current remained for approximately 30 hours before the mutant phenotype returned. The injection of calmodulin isolated from pantophobiac had no effect. These results imply that calmodulin is required for the function or regulation of the Ca²⁺-dependent K⁺ current in Paramecium.