Molecular biology has shown there to be a great diversity of potassium channel isoforms. Among the simplest structurally are the inward rectifier potassium channel, KCNJ gene family. These channels are open in the region of the resting potential, a potential that they therefore help to determine. Some 14 genes are known for this family, classified into 7 subfamilies in terms of sequence homology or identity. These subfamilies are identified as Kir1.0 through Kir7.0 (for review see Stanfield et al., 2002).
Inward rectifier channels are tetramers of pore-forming subunits with two transmembrane domains (M1 and M2) separated by a P-region that forms the most selective part of the pore (Fig. 1). Significantly more than half the molecular mass is made up by the intracellular NH2 and particularly the COOH terminus. The X-ray structure of a bacterial homologue (KirBac1.1) shows that the NH...
