Pulmonary arterial hypertension (PAH) is a rare but fatal disease with an annual mortality rate of 15% despite current therapies. Uncontrolled proliferation of pulmonary artery smooth muscle cells (PASMCs) results in adverse vascular remodeling contributing to PAH. Understanding the mechanisms of PASMC proliferation may identify new targets for treatment. Chloride currents/channels (ICl) are expressed in PASMCs and their roles in proliferation have been suggested based on their importance in resting membrane potential and cell volume regulation. The present study explored the role of ICl in proliferation in rat and human PASMCs. We found that either nonspecific ICl inhibitors (DIDS or NPPB) or a putative specific blocker of swelling-activated ICl (ICl,swell) reduced proliferation of PASMCs cultured in serum-containing media. Patch-clamp studies showed that proliferating PASMCs had increased baseline ICl and ICl,swell in association with depolarized membrane potentials. Quantitative real-time RT-PCR studies identified expressions of CLC-3, a candidate gene of ICl,swell, and several other CLC genes in proliferating PASMCs. While selective knockdown of CLC-3 with lentiviral shRNA reduced PASMC proliferation, it had no effect on ICl,swell. These findings are consistent with the conclusion that ICl regulate proliferation of PASMCs and suggest that selective ICl inhibition may be useful in treating pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a rare but fatal disease with an annual mortality rate of 15% despite current therapies. Uncontrolled proliferation of pulmonary artery smooth muscle cells (PASMCs) results in adverse vascular remodeling contributing to PAH. Understanding the mechanisms of PASMC proliferation may identify new targets for treatment. Chloride currents/channels (ICl) are expressed in PASMCs and their roles in proliferation have been suggested based on their importance in resting membrane potential and cell volume regulation. The present study explored the role of ICl in proliferation in rat and human PASMCs. We found that either nonspecific ICl inhibitors (DIDS or NPPB) or a putative specific blocker of swelling-activated ICl (ICl,swell) reduced proliferation of PASMCs cultured in serum-containing media. Patch-clamp studies showed that proliferating PASMCs had increased baseline ICl and ICl,swell in association with depolarized membrane potentials. Quantitative real-time RT-PCR studies identified expressions of CLC-3, a candidate gene of ICl,swell, and several other CLC genes in proliferating PASMCs. While selective knockdown of CLC-3 with lentiviral shRNA reduced PASMC proliferation, it had no effect on ICl,swell. These findings are consistent with the conclusion that ICl regulate proliferation of PASMCs and suggest that selective ICl inhibition may be useful in treating pulmonary arterial hypertension.