Relationship of intracellular free Ca2+ concentration and calcium-activated chloride channels of pulmonary artery smooth muscle cells in rats under hypoxic conditions

Revisiting the mechanism of hypoxic pulmonary vasoconstriction using isolated perfused/ventilated mouse lung

Hypoxic Pulmonary Vasoconstriction (HPV) is an important physiological mechanism of the lungs that matches perfusion to ventilation thus maximizing O2 saturation of the venous blood within the lungs. This study emphasizes on principal pathways in the initiation and modulation of hypoxic pulmonary vasoconstriction with a primary focus on the role of Ca2+ signaling and Ca2+ influx pathways in hypoxic pulmonary vasoconstriction. We used an ex vivo model, isolated perfused/ventilated mouse lung to evaluate hypoxic pulmonary vasoconstriction. Alveolar hypoxia (utilizing a mini ventilator) rapidly and reversibly increased pulmonary arterial pressure due to hypoxic pulmonary vasoconstriction in the isolated perfused/ventilated lung. By applying specific inhibitors for different membrane receptors and ion channels through intrapulmonary perfusion solution in isolated lung, we were able to define the targeted receptors and channels that regulate hypoxic pulmonary vasoconstriction. We show that extracellular Ca2+ or Ca2+ influx through various Ca2+-permeable channels in the plasma membrane is required for hypoxic pulmonary vasoconstriction. Removal of extracellular Ca2+ abolished hypoxic pulmonary vasoconstriction, while blockade of L-type voltage-dependent Ca2+ channels (with nifedipine), non-selective cation channels (with 30 µM SKF-96365), and TRPC6/TRPV1 channels (with 1 µM SAR-7334 and 30 µM capsazepine, respectively) significantly and reversibly inhibited hypoxic pulmonary vasoconstriction. Furthermore, blockers of Ca2+-sensing receptors (by 30 µM NPS2143, an allosteric Ca2+-sensing receptors inhibitor) and Notch (by 30 µM DAPT, a γ-secretase inhibitor) also attenuated hypoxic pulmonary vasoconstriction. These data indicate that Ca2+ influx in pulmonary arterial smooth muscle cells through voltage-dependent, receptor-operated, and store-operated Ca2+ entry pathways all contribute to initiation of hypoxic pulmonary vasoconstriction. The extracellular Ca2+-mediated activation of Ca2+-sensing receptors and the cell-cell interaction via Notch ligands and receptors contribute to the regulation of hypoxic pulmonary vasoconstriction.

TMEM16A regulates the cell cycle of pulmonary artery smooth muscle cells in high-flow-induced pulmonary arterial hypertension rat model

High-flow-induced pulmonary arterial hypertension (PAH) has attained global notoriety, the mechanism of which remains elusive. The present study investigated the regulation of Anoctamin-1, also known as transmembrane member 16A (TMEM16A), in the cell cycle progression of pulmonary artery smooth muscle cells (PASMCs) from a PAH rat model induced by high pulmonary blood flow. A total of 30 Sprague-Dawley rats were randomly assigned into control, sham and shunt groups. A rat model of high pulmonary blood flow-induced PAH was established by surgery using abdominal aorta-inferior vena cava fistula. Right ventricular pressure, right ventricular hypertrophy index and pulmonary arteriole structural remodeling were assessed 11 weeks following operation. The cell cycle statuses of PASMCs was assessed via flow cytometry, whereas western blot analysis was performed to measure the expression of cyclin D1, CDK2, p27KIP and cyclin E in primary PASMCs isolated from rats. The expression of cyclin E and cyclin D1 was revealed to be increased in the shunt group compared with the control group, which was accompanied with an increased expression of TMEM16A in the shunt group. Changes in the ratio of PASMCs in the G0/G1, S and G2/M phases of cycle induced by PAH were reversed by TMEM16A knockdown. The expression of cyclin E and cyclin D1 in the shunt group was significantly higher compared with the control group in vitro, which was reversed by TMEM16A-siRNA transfection. In conclusion, TMEM16A may be involved in high pulmonary blood flow-induced PAH by regulating PASMC cell cycle progression.

Chronic hypoxia-induced upregulation of Ca2+-activated Cl- channel in pulmonary arterial myocytes: a mechanism contributing to enhanced vasoreactivity

Chronic hypoxic pulmonary hypertension (CHPH) is associated with altered expression and function of cation channels in pulmonary arterial smooth muscle cells (PASMCs), but little is known for anion channels. The Ca(2+)-activated Cl(-) channel (CaCC), recently identified as TMEM16A, plays important roles in pulmonary vascular function. The present study sought to determine the effects of chronic hypoxia (CH) on the expression and function of CaCCs in PASMCs, and their contributions to the vascular hyperreactivity in CHPH. Male Wistar rats were exposed to room air or 10% O(2) for 3–4 weeks to generate CHPH. CaCC current (I(CI.Ca)) elicited by caffeine-induced Ca(2+) release or by depolarization at a constant high [Ca(2+)](i) (500 or 750 nm) was significantly larger in PASMCs of CH rats compared to controls. The enhanced I(CI.Ca)) density in CH PASMCs was unrelated to changes in amplitude of Ca(2+) release, Ca(2+)-dependent activation, voltage-dependent properties or calcineurin-dependent modulation of CaCCs, but was associated with increased TMEM16A mRNA and protein expression. Maximal contraction induced by serotonin, an important mediator of CHPH, was potentiated in endothelium-denuded pulmonary arteries of CH rats. The enhanced contractile response was prevented by the CaCC blockers niflumic acid and T16A(inh)-A01, or by the L-type Ca(2+) channel antagonist nifedipine. The effects of niflumic acid and nifedipine were non-additive. Our results demonstrate for the first time that CH increases I(CI.Ca) density, which is attributable to an upregulation of TMEM16A expression in PASMCs. The augmented CaCC activity in PASMCs may potentiate membrane depolarization and L-type channel activation in response to vasoconstrictors and enhance pulmonary vasoreactivity in CHPH.

Stimulation of regulatory volume increase (RVI) in avian articular chondrocytes by gadolinium chloride

Chondrocytes, the resident cell-type of articular cartilage, are responsible for the regulation of the extracellular matrix (ECM) in response to their physico-chemical environment. Due to the nature of cartilage loading, chondrocytes are exposed to constant changes in extracellular osmolality with a gradual increase throughout the day. As an increase in osmolality attenuates matrix synthesis, we have studied cell volume regulation (regulatory volume increase (RVI)) after hypertonic challenge and the regulation of RVI by the actin cytoskeleton. Using freshly isolated avian articular chondrocytes, changes in actin organisation were studied by confocal laser scanning microscopy following a 43% increase in extracellular osmolality. Using calcein-loading chondrocytes, the capacity for RVI was determined and the rate of volume recovery (t1/2) mathematically extrapolated. Following an increase in extracellular osmolality there was a significant increase (p < 0.05) in cortical actin, inhibited by the removal of extracellular calcium EGTA or by the addition of 100 µmol·L–1 gadolinium chloride. Most cells exhibited slow RVI (t1/2 = 55.5 ± 5.5 min), whereby inhibition of actin polymerisation by gadolinium chloride or the removal of extracellular calcium significantly increased the rate of volume recovery via a bumetanide-sensitive pathway (t1/2 of 29.6 ± 6.5 min and 13.8 ± 3.1 min, respectively). These data suggest the Na+–K+–2Cl– (NKCC) co-transporter regulated by the actin cytoskeleton is involved in avian chondrocyte RVI.