Regional and cellular expression patterns of four K+ channel mRNAs in the adult rat brain

Potassium (K+) channels are involved in the modulation and fine tuning of the excitable properties of neurons and glia in the nervous system. In the present report, in situ hybridization histochemistry was used to determine the regional and cellular distribution patterns in the adult rat brain of four mRNAs encoding subunits of voltage-gated K+ channels. These are Kv1.1, Kv1.6, K13 and IK8. All K+ channels examined showed distinct yet overlapping expression patterns. Expression of Kv1.1 mRNA was high in cells of certain motor-related structures of the brainstem. Kv1.6 mRNA expression was observed in cerebellar Purkinje cells and in various olfactory and amygdaloid structures. K13 was the only mRNA expressed in both neuronal and non-neuronal cell populations, including the cells of choroid plexus and pia. IK8 expression was observed only in the forebrain structures. In many brain regions, mRNAs for Kv1.1 and Kv1.6, both encoding K+ channel subunits belonging to the Shaker subfamily, were co-expressed, a necessary condition for heteromultimer formation.

Expression of a minimal K+ channel protein in mammalian cells and immunolocalization in guinea pig heart

The minimal K+ channel protein (minK, also called IsK) is structurally dissimilar to other cloned voltage-gated ion channels. minK is a 15-kD polypeptide with only one potential transmembrane helix. Published data suggest that the current associated with minK expression in Xenopus oocytes may be related to the slow cardiac delayed rectifier K+ current (IKs). However, the fact that minK expression has been limited exclusively to Xenopus oocytes has caused continuing concern about the nature of this protein and its molecular link to known mammalian K+ channels. We report in the present study the first expression of minK activity in transiently transfected mammalian (HEK 293) cells and demonstrate that the characteristics of the expressed minK current are similar to those of IKs recorded from guinea pig heart cells under similar experimental conditions. We also show that an antibody directed against the minK channel protein reacts with a surface antigen on adult guinea pig ventricular myocytes and sinoatrial nodal cells, where IKs is the dominant outward K+ current. The data provide strong evidence that a minK-like protein underlies IKs.