Am. J. Respir. Cell Mol. Biol., Volume 26, Number 3, March, 2002 371-379

Inward Rectifier K⁺ Current in Human Bronchial Smooth Muscle Cells
Inhibition with Antisense Oligonucleotides Targeted to Kir2.1 mRNA

Hitoshi Oonuma, Kuniaki Iwasawa, Haruko Iida, Taiji Nagata, Hiroyuki Imuta, Yutaka Morita, Kazuhiko Yamamoto, Ryozo Nagai, Masao Omata, and Toshiaki Nakajima

Departments of Respiratory and Cardiovascular Medicine and of Gastroenterology, University of Tokyo, Graduate School of Medicine, Tokyo, Japan

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 Ba²⁺. The IC₅₀ value of external Ba²⁺ was ~ 1.3 µm. 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 Ba²⁺ 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.