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

Abstract

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-binding domain conserved in all mammalian SK channel sequences were employed to detect SK DNA in a cDNA library from rat SCG. Only a single band, corresponding to a fragment of the rSK3 gene, was amplified. 3 Northern blot analysis employing a PCR-generated rSK3 fragment showed the presence of mRNA coding for SK3 in SCG as well in other rat peripheral tissues 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 with, that of the previously reported rSK3 gene. 5 Expression of the rSK3 gene in mammalian cell lines (CHO, HEK cells) caused the appearance of a K⁺ conductance with SK channel properties. 6 The application of selective SK blocking agents (including apamin, scyllatoxin and newer non-peptidic compounds) showed these homomeric SK3 channels to have essentially the same pharmacological characteristics as the SCG afterhyperpolarization, but to differ from those of homomeric SK1 and SK2 channels. 7 Immunohistochemistry using a rSK3 antipeptide antibody revealed the presence of SK3 protein in the cell bodies and processes of cultured SCG neurones. 8 Taken together, these results identify SK3 as a major component of the SK channels responsible for the afterhyperpolarization of cultured rat SCG neurones.