Rationale: An increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC proliferation and pulmonary vascular remodeling. The dihydropyridine Ca(2+) channel blockers, such as nifedipine, have been used for treatment of idiopathic pulmonary arterial hypertension (IPAH).
Objective: Our previous study demonstrated that the Ca(2+)-sensing receptor (CaSR) was upregulated and the extracellular Ca(2+)-induced increase in [Ca(2+)](cyt) was enhanced in PASMC from patients with IPAH and animals with experimental pulmonary hypertension. Here, we report that the dihydropyridines (eg, nifedipine) increase [Ca(2+)](cyt) by activating CaSR in PASMC from IPAH patients (in which CaSR is upregulated), but not in normal PASMC.
Methods and results: The nifedipine-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC was concentration dependent with a half maximal effective concentration of 0.20 µmol/L. Knockdown of CaSR with siRNA in IPAH-PASMC significantly inhibited the nifedipine-induced increase in [Ca(2+)](cyt), whereas overexpression of CaSR in normal PASMC conferred the nifedipine-induced rise in [Ca(2+)](cyt). Other dihydropyridines, nicardipine and Bay K8644, had similar augmenting effects on the CaSR-mediated increase in [Ca(2+)](cyt) in IPAH-PASMC; however, the nondihydropyridine blockers, such as diltiazem and verapamil, had no effect on the CaSR-mediated rise in [Ca(2+)](cyt).
Conclusions: The dihydropyridine derivatives increase [Ca(2+)](cyt) by potentiating the activity of CaSR in PASMC independently of their blocking (or activating) effect on Ca(2+) channels; therefore, it is possible that the use of dihydropyridine Ca(2+) channel blockers (eg, nifedipine) to treat IPAH patients with upregulated CaSR in PASMC may exacerbate pulmonary hypertension.