A gamma ray-induced non-excitable membrane mutant in Paramecium caudatum: A behavioral and genetic analysis

A new CNR (caudatum non-reversal) mutant of Paramecium caudatum was isolated after gamma ray mutagenesis. This CNR lacks not only the transient inward Ca²⁺ current but also the sustained Ca²⁺ current. It was shown to complement the three known CNR mutants of P. caudatum (cnrA, cnrB and cnrC) by crossbreeding analyses. Thus, this new mutant belongs to a 4th CNR locus, designated cnrD. The defect of cnrD can be partially rescued by microinjection of cytoplasm from any of the three CNR mutants or the three Pawns (pwA, pwB and pwC) in P. tetraurelia. Since the three CNR genes have been shown to be different from the three Pawn genes by cytoplasmic complementation test (Haga et al. 1983), this result suggests that cnrD is the 7th non-excitable mutant in Paramecium. Thus, there are at least seven genes controlling Ca²⁺ channel function in Paramecium.