PDGFRB and pulmonary arterial hypertension: Protein expression of platelet-derived growth factor receptor beta (PDGFR-β) was increased under basal conditions in PAH-hPASMCs versus control hPASMCs, whereas in control hPASMCs serotonin increased expression of PDGFR-β where this increase was attenuated in the presence of 5-HT1BR antagonist SB224289 (Figure IVB in the online-only Data Supplement).