Depressed Serotonin-Induced Vasocontraction and K+-Channel Inhibition by KMUP-1 in Pulmonary Artery

BN WU1, ZK DAI2, YW LIU1, SL CHIA3, IJ CHEN1. 1Kaohsiung Medical University, Department of Pharmacology, Kaohsiung 807, Taiwan, 2Kaohsiung Medical University Hospital, Department of Pediatrics, Kaohsiung 807, Taiwan, 3Kaohsiung Medical University Hospital, Department of Pharmacy, Kaohsiung 807, Taiwan

Serotonin (5-hydroxytryptamine, 5-HT) is a potent pulmonary vasoconstrictor and promotes pulmonary arterial smooth muscle cells (PASMCs) proliferation. 5-HT-induced K+ channels inhibition would increase the [Ca2+]i in PASMCs, which is a major trigger for pulmonary vasocontraction and development of pulmonary arterial hypertension (PAH). This study investigated whether KMUP-1 (7-[2-[4-(2-chlorobenzene)piperazinyl]ethyl]-1,3-dimethylxanthine), a K+ channel opener, reduces pulmonary vasocontractions in isolated pulmonary arteries (PAs) and attenuates 5-HT-inhibited K+-channel activities in PASMCs. Data are expressed as means ± s.e., n=6. Statistical differences were determined by one-way ANOVA followed by Dunnett’s or Tukey test. PASMCs were incubated with 5-HT (10 μM) or 5-HT plus KMUP-1 (1 μM) for 24 h. In isolated PA rings, KMUP-1 (0.1, 1, 10 μM) reduced 5-HT (100 μM)-induced contractile responses in a dose-dependent manner (from 128.7+8.4% to 91.6+5.6%, 47.8+11.4%, 19.6+5.9%, n=6, p<0.05). The effects of KMUP-1 were reversed by K+ channel inhibitors (tetraethylammonium, 10 mM, 4-aminopyridine, 5 mM, and paxilline, 10 μM). Additionally, KMUP-1 (0.1, 1, 10 μM) also dose-dependently attenuated 5-HT (10 μM)-inhibited voltage-gated K+-channel (Kv1.5 and Kv2.1) (39.7+9.6% and 46.8+4.3% to 48.4+6.0%, 71.4+6.5%, 81.5+9.3% and 57.8+6.6%, 78.5+7.8%, 83.2+8.7%, n=6, p<0.05) and large-conductance Ca2+-activated K+-channel (BKCa) proteins in PASMCs (from 31.0+6.8% to 51.8+6.1%, 80.1+7.6%, 87.9+5.1%, n=6, p<0.05) and those were confirmed by immunofluorescent localization. In conclusion, KMUP-1 attenuates 5-HT-induced vasocontraction and K+-channel inhibition, which might have the ability to prevent the development of PAH.