Cloning and functional expression of a human gene, hIRK1, encoding the heart inward rectifier K+-channel

We have isolated a cDNA clone encoding a human inward rectifier potassium channel (hIRK1). The nucleotide (nt) sequence of the coding region is 88% similar to the mouse clone with only seven amino-acid (aa) differences. The hIRK1 cRNA initially expressed low levels of protein in a wheat germ system and in Xenopus oocytes. The addition of a SmaI site 3' to the poly(A) tail increased the expression at least tenfold. Xenopus oocytes injected with the hIRK1 cRNA developed resting potentials that averaged -96 mV and a large inward current that was blocked by Ba2+ or Cs+. The hIRK1 EK shifted 54.6 mV per decade change in [K]o, and its channel conductance increased with [K]o by a 0.3 exponent factor. Above EK, the hIRK1 I-V relation has a distinct 'N'-shape. Cell-attached single-channel conductance in 140 mM K+ pipette solution averaged 29 pS. The negative resting potential and the 'N'-shape I-V relation of hIRK1 closely resemble that of the native cardiac inward rectifier IK1.