Decreased expression of voltage-gated K⁺ channels in pulmonary artery smooth muscles cells in nitrofen-induced congenital diaphragmatic hernia in rats

Abstract

The newborn with congenital diaphragmatic hernia (CDH) is at high risk of developing persistent pulmonary hypertension (PPH). Recently, smooth muscle K⁺ channels have been implicated in hypoxic pulmonary vasoconstriction in adults. We hypothesized that the hyperreactivity of the newborn pulmonary vasculature in CDH might reflect a relatively low level of smooth muscle K⁺ channel activity because of hypoxemia, which could give rise to excessive smooth muscle cell depolarisation and lead to failure of the pulmonary vasculature to adapt to extrauterine life. We therefore investigated K⁺ channel subunits in pulmonary artery smooth muscle cells (PASMC) in the nitrofen-induced CDH lung in rats. The CDH model was induced in pregnant rats after administration of 100 mg nitrofen on day 9.5 of gestation (term = 22 days). Dexamethasone (0.25 mg/kg) was given on days 18.5 and 19.5 of gestation. Cesarean section was performed on day 21. Fetuses were divided into three groups: group I, normal control; group II, nitrofen-induced CDH; and group III, nitrofen-induced CDH with antenatal dexamethasone treatment. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of the potassium channels Kv1.2, Kv2.1, and KvCa mRNA. Indirect immunohistochemistry was performed using a laser scanning confocal microscope with anti-Kv1.2, -Kv2.1, and -KvCa antibodies. In the CDH lung, Kv1.2, Kv2.1, and KvCa immunoreactivity was markedly decreased in PASMC compared with controls. Relative mRNA levels of potassium channel anti-Kv1.2, -Kv2.1, and -KvCa were significantly decreased in the CDH lung compared with controls ( p <0.05). Dexamethasone treatment increased Kv1.2, Kv2.1, and KvCa immunoreactivity and mRNA levels in the CDH lung. Changes in voltage-gate K⁺ channel subunits expression in the CDH lung suggest that potassium channels may play an important role in the development of pulmonary hypertension. Antenatal dexamethasone may modulate pulmonary vascular tone in the CDH hypoplastic lung by selectively upregulating local expression of Kv1.2, Kv2.1, and KvCa.