Inwardly rectifying potassium channels in lens epithelium are from the IRK1 (Kir 2.1) family

Lens epithelial cells from many species contain inwardly rectifying K+ channels. The channels are highly selective for K+ over Na+. They have a conductance of 27-30 pS in symmetrical 150 mM K+ solutions. The conductance to inwardly flowing current depends on the external [K+], being 1/2 maximal at about 50 mM and maximal by 110-150 mM. The amino acid sequences from lens epithelium (eight different species) show at least 98% sequence homology to each other and to the potassium channel known as IRK1 (Kir 2.1). Cloned channels from chick, rabbit, and human lens epithelium all make functional channels when their cDNA is transfected into HEK-293 or tsA-201 cells. Human lens inward rectifiers when engineered as fusion proteins with green fluorescent protein (GFP) also make functional channels. In addition, their localization in the membrane and in intracellular organelles can be demonstrated by fluorescence microscopy.