Abstract 4923: Prostacyclin Analogues Activates Calcium-dependent Potassium (KCa) Channels via PPAR β/δ in Pulmonary Artery
Pulmonary hypertension is associated with vasoconstriction, thrombosis and proliferation, and the lack of endogenous prostacyclin. Prostacyclin and its analogues are potent vasodilators, representing an important pillar of modern therapy of this devastating disease. Potassium channels determine the membrane potential of pulmonary artery smooth muscle cells (PASMCs) and are important controllers of their calcium homeostasis and consequently the pulmonary arterial tone. In the present study, we investigated the signaling pathway and effects of the stable prostacyclin analogues treprostinil and iloprost in primary human PASMCs and isolated rat pulmonary artery. We employed the whole-cell patch-clamp technique combined with small interfering (si)RNA and live-cell calcium imaging on human PASMCs and the myograph-mounted isolated intrapulmonary artery model. We found that treprostnil (10 nM) and iloprost (10 nM) hyperpolarized primary human PASMCs (13.1 ± 2.2 mV, p < 0.01 and 15.7 ± 2 mV, p < 0.01 respectively, n = 6 for each group) and activated KCa (IC50 = 0.2 ± 0.05 nM and IC50 = 0.5 ± 0.2 nM respectively, n = 5 for each group) at clinically relevant concentrations. The IP receptor antagonist RO1138452 (10 μM) and PKA blocker KT5720 (1 mM) abolished these effects. In the siRNA-transfected cells no enhancement of KCa current was detected. The novel PPARβ/δ antagonist GSK0660 (10 nM), abolished the activation of KCa current by iloprost or treprostinil, whereas the selective PPARβ/δ agonist GW0742 (10 nM) activated the KCa current. Calcium imaging measurements supported these data showing that GW0742 reduced the basal intracellular calcium concentration by 9.41±2.99 % (n = 25, p < 0.01) compared to the baseline in human PASMCs. Consequently, GW0742 caused relaxation in U46619-preconstricted rat intrapulmonary arteries (IC50 = 9.42 μM, n = 5). This is the first study implicating KCa in the prostacyclin analogue- mediated hyperpolarization via PPARβ/δ in human PASMCs. This might represent a novel pathway related to the vasodilating effects of prostanoids.