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Iida H, Jo T, Iwasawa K, Morita T, Hikiji H, Takato T, Toyo-Oka T, Nagai R, Nakajima T: Molecular and pharmacological characteristics of transient voltage-dependent K+ currents in cultured human pulmonary arterial smooth muscle cells. Br J Pharmacol. 2005 Sep;146(1):49-59.
The A-type voltage-dependent K (+) current (I (A)) has been identified in several types of smooth muscle cells including the pulmonary artery (PA), but little is known about the pharmacological and molecular characteristics of I (A) in human pulmonary arterial smooth muscle cells (hPASMCs). We investigated I (A) expressed in cultured PASMCs isolated from the human main pulmonary artery, using patch-clamp techniques, reverse transcriptase-polymerase chain reaction (RT-PCR), quantitative real-time RT-PCR and immunocytochemical studies. With high EGTA and ATP in the pipette, the outward currents were dominated by a transient K (+) current (I (A)), followed by a relatively small sustained outward current (I (K)). I (A) was inhibited by 4-aminopyridine (4-AP) concentration-dependently, and could be separated pharmacologically into two components by tetraethylammonium (TEA) sensitivity. A component was sensitive to TEA, and the second component was insensitive to TEA. I (A) was inhibited by blood depressing substrate (BDS)-II, a specific blocker of K (V) 3.4 subunit, and phrixotoxin-II, a specific blocker of K (V) 4.2 and 4.3. Flecainide inhibited I (A) concentration-dependently, but it inhibited it preferentially in the presence of TEA (TEA-insensitive I (A)). Systematic screening of expression of K (V) genes using RT-PCR showed the definite presence of transcripts of the I (A)-encoding genes for K (V) 3.4, K (V) 4.1, K (V) 4.2 and K (V) 4.3 as well as the I (K)-encoding genes for K (V) 1.1, K (V) 1.5 and K (V) 2.1. The real-time RT-PCR analysis showed that the relative abundance of the encoding genes of I (A) alpha-subunit and K (V) channel-interacting proteins (KChIPs) was K (V) 4.2 > K (V) 3.4 > K (V) 4.3 (long) > K (V) 4.1, and KChIP3 >> KChIP2, respectively. The presence of K (V) 3.4, K (V) 4.2 and K (V) 4.3 proteins was also demonstrated by immunocytochemical studies, and confirmed by immunohistochemical staining using intact human PA sections. These results suggest that I (A) in cultured hPASMCs consists of two kinetically and pharmacologically distinct components, probably K (V) 3.4 and K (V) 4 channels. |
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