Potassium inward rectifier K(IR)2.1 channels contribute to the stable resting membrane potential in a variety of muscle and neuronal cell-types. Mutations in the K(IR)2.1 gene KCNJ2 have been associated with human disease, such as cardiac arrhythmias and periodic paralysis. Crystal structure and homology modelling of K(IR)2.1 channels combined with functional current measurements provided valuable insights in mechanisms underlying channel function. K(IR)2.1 channels have been cloned and analyzed from all main vertebrate phyla, except reptilians. To address this lacuna, we set out to clone reptilian K(IR)2.1 channels. Using a degenerated primer set we cloned the KCNJ2 coding regions from muscle tissue of turtle, snake, bear, quail and bream, and compared their deduced amino acid sequences with those of K(IR)2.1 sequences from 26 different animal species obtained from Genbank. Furthermore, expression constructs were prepared for functional electrophysiological studies of ectopically expressed K(IR)2.1 ion channels. In general, ICCNJ2 gene evolution followed normal phylogenetic patterns, however turtle K(IR)2.1 ion channel sequence is more homologues to avians than to snake. Alignment of all 31 K(IR)2.1 sequences showed that all disease causing K(IR)2.1 mutations, except V93I, V123G and N318S, are fully conserved. Homology models were built to provide structural insights into species specific amino acid substitutions. Snake K(IR)2.1 channels became expressed at the plasmamembrane and produced typical barium sensitive (IC50 similar to 6 mu M) inward rectifier currents. (C) 2014 Elsevier Inc. All rights reserved.