thapsigargin and Lung-Diseases--Obstructive

The molecular mechanisms by which endothelin (ET)-1 induces pulmonary hypertension are poorly understood. We investigated the effects of ET-1 on outward K+ currents of normoxic and chronically hypoxic human pulmonary arterial (PA) smooth muscle cells (HPSMCs). In normoxic HPSMCs, ET-1 has dual effects. In intact cells, 5 nM ET-1 activates the large-conductance and Ca2+-activated K+ (KCa)-channel current [IK(Ca)] by increasing intracellular Ca2+ concentration, whereas it directly inhibits IK(Ca) in isolated membrane patches. At a higher concentration (10 nM), ET-1-induced IK(Ca) inhibition predominates. In hypoxic HPSMCs, ET-1 at 5 nM significantly reduces IK(Ca). The ETA-receptor antagonist BQ-123 reverses the ET-1-induced decrease in IK(Ca). Chronic BQ-123 treatment also prevents the hypoxia-induced decrease in IK(Ca). In PA rings obtained from human organ donors, ET-1 causes a concentration-dependent increase in tension. The ET-1-mediated increase in tension is reversed by a KCa-channel agonist. The increase in tension at the highest concentration studied (9 nM) was more pronounced in PA rings obtained from patients with chronic obstructive pulmonary disease. These results imply that an ET-1-induced decrease in IK(Ca) contributes to chronic hypoxia-induced pulmonary hypertension.

Topics: 4-Aminopyridine; Analysis of Variance; Cell Hypoxia; Cells, Cultured; Charybdotoxin; Dehydroepiandrosterone; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelin-1; Humans; In Vitro Techniques; Kinetics; Large-Conductance Calcium-Activated Potassium Channels; Lung Diseases, Obstructive; Membrane Potentials; Muscle Contraction; Muscle, Smooth, Vascular; Patch-Clamp Techniques; Peptides, Cyclic; Potassium Channels; Potassium Channels, Calcium-Activated; Pulmonary Artery; Receptor, Endothelin A; Thapsigargin