Vardenafil ameliorates calcium mobilization in pulmonary artery smooth muscle cells from hypoxic pulmonary hypertensive mice.

BACKGROUND AND AIMS: Vardenafil has been found to be potent in pulmonary hypertension; however, the underlying mechanisms remain poorly understood. To address this issue, we investigated the underlying mechanisms of vardenafil in the contribution of Ca(2+) signaling and mobilization in modifying vasoconstriction of pulmonary arteries in hypoxic mice.
METHODS: Hemodynamic measurements and morphological studies were performed. Muscle tension was measured by PowerLab system. I(Ca,L) was recorded using a perforated patch-clamp technique. [Ca(2+)](i) was measured using a fluorescence imaging system.
RESULTS: Vardenafil greatly inhibited RVSP increases, RV hypertrophy and ameliorated pulmonary artery remodeling in response to chronic hypoxia. Membrane depolarization following 50 mM high K(+)-caused muscle contraction significantly decreased from 101.7 ± 10.1 in the hypoxia group to 81.8 ± 5.0 mg in hypoxia plus vardenafil arteries. Fifty mM high K(+)-elicited increase [Ca(2+)](i) was markedly decreased from 610.6 ± 71.8 in hypoxia cells to 400.3 ± 47.2 nM in hypoxia plus vardenafil cells. Application of vardenafil greatly inhibited the density of I(Ca,L) by 37.7% compared with that in the hypoxia group. Administration of 1 μM phenylephrine to stimulate α(1)-adrenergic receptor resulted in a smaller increase in [Ca(2+)](i) in hypoxia plus vardenafil cells than that in hypoxia cells. One hundred μM ATP-mediated increase in [Ca(2+)](i) was also inhibited in vardenafil-hypoxia group (from 625.8 ± 62.3 to 390.9 ± 38.1 nM), suggesting that internal calcium reserves contribute to neurotransmitter-induced Ca(2+) release from the SR through IP(3)Rs in PASMCs.
CONCLUSIONS: Vardenafil may effectively block Ca(2+) influx through L-type Ca(2+) channel and inhibit the Ca(2+) release from SR through IP(3)Rs, thus enhancing its vasorelaxation of pulmonary arteries under hypoxia conditions.