INWARD RECTIFIER POTASSIUM CHANNELS - CLONING, EXPRESSION AND STRUCTURE-FUNCTION STUDIES

A PCR-based cloning strategy was used to identify novel subunits of th e two-transmembrane domain inward rectifier potassium channel family f rom rat brain, heart, and skeletal muscle. When expressed in Xenopus o ocytes, two of these clones (Kir4.1 and Kir2.3) gave rise to inwardly rectifying potassium currents. Two-electrode voltage clamp commands to potentials negative to EK evoked inward potassium-selective currents which rapidly reached a peak amplitude and then relaxed to a steady-st ate level. Differences in the extent of current relaxation, the degree of rectification, and the voltage-dependent block by external cesium were detected. Two other members of this family (Kir5.1 and Kir3.4) di d not produce macroscopic currents, when expressed by themselves, yet both subunits modified the currents when coexpressed with other specif ic members of the Kir family. Expression of chimeric subunits between Kir4.1 and either Kir5.1 or Kir3.4 suggested that the transmembrane do mains determine the specificity of subunit heteropolymerization, while the C-terminal domains contribute to alterations in activation kineti cs and rectification. Expression of covalently linked subunits demonst rated that the relative subunit positions, as well as stoichiometry, a ffect heteromeric channel activity.