Danshen, the dried root of Salvia miltiorrhiza, is widely used in clinics in China for treating various diseases, including cardiovascular diseases. Sodium tanshinone IIA sulfonate (STS), a water-soluble derivative of tanshinone IIA isolated as the major active component from Danshen, was recently reported to be effective in attenuating the characteristic pulmonary vascular changes associated with chronically hypoxic pulmonary hypertension (CHPH); however, the underlying detailed mechanisms are poorly understood. In this study, we investigated the effects of STS on basal intracellular Ca 21 concentration ([Ca 21 ] i ) and store-operated Ca 21 entry (SOCE) in distal pulmonary arterial smooth muscle cells (PASMCs) exposed to prolonged hypoxia or isolated from CHPH rats. SOCE measured by Mn 21 quenching of Fura-2 fluorescence in PASMCs from rats exposed to chronic hypoxia (10% O 2 , 21 d) was increased by 59%, and basal [Ca 21 ] i was increased by 119%; this effect was inhibited by intraperitoneal injection of STS. These inhibitory effects of STS on hypoxic increases of SOCE and basal [Ca 21 ] i were associated with reduced expression of canonical transient receptor potential (TRPC)1 and TRPC6 in distal pulmonary arterial smooth muscle and decreases on right ventricular pressure, right ventricular hypertrophy, and peripheral pulmonary vessel thickening. In ex vivo cultured distal PASMCs from normoxic rats, STS (0-25 mM) dose-dependently inhibited hypoxiainduced cell proliferation and migration, paralleled with attenuation in increases of basal [Ca 21 ] i , SOCE, mRNA, and protein expression of TRPC1 and TRPC6. STS also relieved right ventricular systolic pressure, right ventricular hypertrophy, and TRPC1 and TRPC6 protein expression in distal pulmonary arteries in a monocrotaline-induced rat model of pulmonary arterial hypertension. These results indicate that STS prevents pulmonary arterial hypertension development likely by inhibiting TRPC1 and TRPC6 expression, resulting in normalized basal [Ca 21 ] i and attenuated proliferation and migration of PASMCs.Keywords: STS; TRPC; SOCE; pulmonary hypertension Pulmonary arterial hypertension (PAH) is a rare yet life-threatening disease that affects 15 per 1 million adults, according to the most recent estimation in 2008 (1). It is physiologically defined by mean pulmonary arterial pressure of 25 mm Hg or greater at rest and is pathologically characterized by pulmonary vascular remodeling, including smooth muscle hypertrophy and intima thickening. Although significant progress has been made in the past decades in our understanding of PAH and in disease management, the prognosis is still poor, with a 1-year survival rate of 91.0% (2) and 3-year survival rate of 77% or less according to recent investigations (3-5). The principal treatments for PAH rely on approaches targeting the prostacyclin, endothelin, or NO pathways (phosphodiesterase inhibition) or, increasingly, on a combination of them (6-11). Few patients show indication for treatment with calcium channel...
BMP4 acts downstream of HIF-1 and mediates hypoxia-induced up-regulation of TRPC, leading to increased basal [Ca(2+)]i in PASMCs, promoting CHPH pathogenesis.
Chronic hypoxia causes remodeling and alters contractile responses in both pulmonary arteries and pulmonary veins. Although pulmonary arteries have been studied extensively in these disorders, the mechanisms by which pulmonary veins respond to hypoxia and whether these responses contribute to chronic hypoxic pulmonary hypertension remain poorly understood. In pulmonary arterial smooth muscle, we have previously demonstrated that influx of Ca(2+) through store-operated calcium channels (SOCC) thought to be composed of transient receptor potential (TRP) proteins is likely to play an important role in development of chronic hypoxic pulmonary hypertension. To determine whether this mechanism could also be operative in pulmonary venous smooth muscle, we measured intracellular Ca(2+) concentration ([Ca(2+)](i)) by fura-2 fluorescence microscopy in primary cultures of pulmonary venous smooth muscle cells (PVSMC) isolated from rat distal pulmonary veins. In cells perfused with Ca(2+)-free media containing cyclopiazonic acid (10 μM) and nifedipine (5 μM) to deplete sarcoplasmic reticulum Ca(2+) stores and block voltage-dependent Ca(2+) channels, restoration of extracellular Ca(2+) (2.5 mM) caused marked increases in [Ca(2+)](i), whereas MnCl(2) (200 μM) quenched fura-2 fluorescence, indicating store-operated Ca(2+) entry (SOCE). SKF-96365 and NiCl(2), antagonists of SOCC, blocked SOCE at concentrations that did not alter Ca(2+) responses to 60 mM KCl. Of the seven known canonical TRP (TRPC1-7) and six vanilloid-related TRP channels (TRPV1-6), real-time PCR revealed mRNA expression of TRPC1 > TRPC6 > TRPC4 > TRPC2 ≈ TRPC5 > TRPC3, TRPV2 > TRPV4 > TRPV1 in distal PVSMC, and TRPC1 > TRPC6 > TRPC3 > TRPC4 ≈ TRPC5, TRPV2 ≈ TRPV4 > TRPV1 in rat distal pulmonary vein (PV) smooth muscle. Western blotting confirmed protein expression of TRPC1, TRPC6, TRPV2, and TRPV4 in both PVSMC and PV. Our results suggest that SOCE through Ca(2+) channels composed of TRP proteins may contribute to Ca(2+) signaling in rat distal PV smooth muscle.
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