SK3 is an important component of K+ channels mediating the afterhyperpolarization in cultured rat SCG neurones

1. Our aim was to identify the small-conductance Ca2+-activated K+ channel( s) (SK) underlying the apamin-sensitive afterhyperpolarization (AHP) in rat superior cervical ganglion (SCG) neurones. 2. Degenerate oligonucleotide primers designed to the putative calmodulin-b inding domain conserved in all mammalian SK channel sequences were employed to detect SK DNA in a cDN,A library from rat SCG. Only a single band, corr esponding to a fragment of the rSK3 gene, was amplified. 3. Northern blot analysis employing a PCR-generated rSK3 fragment showed th e presence of mRNA coding for SK3 in SCG as well in other rat peripheral ti ssues including adrenal gland and liver. 4. The same rSK3 fragment enabled the isolation of a full-length rSK3 cDNA from the library. Its sequence was closely similar to, but not identical wi th, that of the previously reported rSK3 gene. 5. Expression of the rSK3 gene in mammalian cell lines (CHO, HEK cells) cau sed the appearance of a K+ conductance with SK channel properties. 6. The application of selective SK blocking agents (including apamin, scyll atoxin and newer nonpeptidic compounds) showed these homomeric SK3 channels to have essentially the same pharmacological characteristics as the SCG af terhyperpolarization, but to differ from those of homomeric SK1 and SK2 cha nnels. 7. Immunohistochemistry using a rSK3 antipeptide antibody revealed the pres ence of SK3 protein in the cell bodies and processes of cultured SCG neuron es. 8. Taken together, these results identify SK3 as a major component of the S K channels responsible for the afterhyperpolarization of cultured rat SCG n eurones.