Morphometric analysis of pulmonary vasculature in Kcnmb1−/− mice. A: Movat pentachrome-stained pulmonary tissues from Kcnmb1+/+ and Kcnmb1−/− mice exposed to normoxia or chronic hypoxia to examine muscularization of peripheral pulmonary arteries (PAs). Magnification ×200; scale bar 25 μm. Quantification of peripheral PA muscularization expressed as the medial thickness index of PA ≤ 100 μm in external diameter (n = 5 per group with 10 fields assessed per mouse). Bars represent means ± SE, §P ≤ 0.05, normoxia vs. hypoxia. B: α-SMA and Von Willebrand Factor (VWF) stained peripheral vessels were counted and categorized into nonmuscularized (NM), partially muscularized (PM), or fully muscularized (FM). Bars represent means ± SE of the number of α-SMA-positive PA ≤ 150 μm in external diameter (n = 3–6 per group with 12 fields assessed per mouse). Within each group, significance was determined as follows: +++P ≤ 0.001, normoxia vs. hypoxia; Kcnmb1−/− PM, ++P ≤ 0.01 normoxia vs. hypoxia; Kcnmb1−/− FM, +P ≤ 0.05, normoxia vs. hypoxia. C: quantification of α-SMA-positive distal PA ≤ 150 μm in external diameter per high-powered field (HPF) in Kcnmb1+/+ and Kcnmb1−/− mice exposed to normoxia or chronic hypoxia. Bars represent means ± SE of the number of α-SMA positive distal PA (n = 5–6 per group with 12 fields assessed per mouse). §§P ≤ 0.01, normoxia vs. hypoxia.