The developmental expression of voltage-sensitive K+ channels was analyzed by Northern blot in mouse skeletal muscle. Of nine Shaker-like genes studied, eight are expressed in this mammalian muscle. Their expression is differentially regulated during development. The mouse cell line C2C12 has been used to study expression of voltage-sensitive K+ channels during in vitro myotube differentiation. Different voltage-sensitive K+ channel messages are also expressed in these cells which display a pattern of expression depending upon the differentiation stage. The message for the very peculiar K+ channel of IsK type could only be detected by polymerase chain reaction on skeletal muscle mRNA.