Inward rectifier K(+) current in human bronchial smooth muscle cells: inhibition with antisense oligonucleotides targeted to Kir2.1 mRNA.

Inward rectifier K(+) (Kir) channels play an important role in forming membrane potential and then modulating muscle tone in certain types of smooth muscles. In cultured human bronchial smooth muscle cells (hBSMCs), Kir current was identified using whole-cell voltage clamp techniques and explored by using RT-PCR analysis of mRNA, Western blotting, and antisense oligonucleotide methods to block the synthesis of Kir channel protein. The K(+) current with strong inward rectification and high K(+) ion selectivity was observed. The current was unaffected by 4-aminopyridine, glibenclamide, and charybdotoxin, and hardly inhibited by tetraethylammonium, but was potently inhibited by extracellular Ba(2+). The IC(50) value of external Ba(2+) was approximately 1.3 microm. RT-PCR analysis of mRNA showed transcripts for Kir2.1, but not Kir1.1, Kir2.2, or Kir2.3. Treatment of cells with antisense oligonucleotides targeted to Kir2.1 resulted in a decrease in the current density of the Kir current and Kir protein expression, as compared with the mismatch-treated cells, whereas the current density of 4-AP-sensitive K(+) currents (K(V)) remained unaffected. The application of Ba(2+) markedly depolarized the membrane. These results demonstrate that Kir channel is present in human bronchial smooth muscle cells, and the Kir2.1 gene encodes the Kir channel protein in these cells.