Blocking K⁺ channels inhibits serum stimulated fibroblast proliferation and p38 map kinase activity in pulmonary artery cells from chronically hypoxic rats

Previous studies have shown that hypoxia inhibits outward K⁺ currents in pulmonary artery smooth muscle cells resulting in contraction (Weir et al FASEB J. 9 183-189 1995). We wished to determine the effect of blocking K⁺ channels on proliferation and p38 MAP kinase in pulmonary artery and systemic artery fibroblasts cultured from chronically hypoxic rats. Methods Fibroblasts were harvested from rat pulmonary artery (RPAF) and aorta (RAF) and utilised between passages 3-10. Cells were obtained from normoxic (N) or chnonically hypoxic (H) rats. Hypoxic rats had been maintained in hypoxic conditions (PO₂=70mmHg) for 2 weeks. Cells were quiesced for 48 hours then stimulated with 5% serum for 24 hours with or without 2mM 4-aminopyridine (a classic Kv channel blocker). Fibroblast replication was measured by [³H]thymidine uptake and p38 activity measured by Western Blot analysis. Results 4-aminopyridine greatly reduced the proliferative effects of serum in both the pulmonary and aortic fibroblasts and completely abolished the increased replication seen in the RPAF cells from chronically hypoxic animals. p38 MAP kinase activity was abolished in pulmonary artery fibroblasts from chronically hypoxic animals. Conclusion. K⁺ currents may play an important role, not only in the pulmonary vasoconstrictive response to hypoxia but also in the proliferative response by pulmonary vascular cells to hypoxia. (Graph Presented).