Chronic intrauterine pulmonary hypertension compromises fetal pulmonary artery smooth muscle cell O 2 sensing

To test the hypothesis that chronic intrauterine pulmonary hypertension (PHTN) compromises pulmonary artery (PA) smooth muscle cell (SMC) O 2 sensing, fluorescence microscopy was used to study the effect of an acute increase in Po 2 on the cytosolic Ca 2+ concentration ([Ca 2+ ] i ) of chronically hypoxic subconfluent monolayers of PA SMC in primary culture. PA SMCs were derived from fetal lambs with PHTN due to intrauterine ligation of the ductus arteriosus. Acute normoxia decreased [Ca 2+ ] i in control but not PHTN PA SMC. In control PA SMC, [Ca 2+ ] i increased after Ca 2+ -sensitive (K Ca ) and voltage-sensitive (K v ) K + channel blockade and decreased after diltiazem treatment. In PHTN PA SMC, K Ca blockade had no effect, whereas K v blockade and diltiazem increased [Ca 2+ ] i . Inhibition of sarcoplasmic reticulum Ca 2+ ATPase activity caused a greater increase in [Ca 2+ ] i in controls compared with PHTN PA SMC. Conversely, ryanodine caused a greater increase of [Ca 2+ ] i in PHTN compared with control PA SMC. K Ca channel mRNA is decreased and K v channel mRNA is unchanged in PHTN PA SMC compared with controls. We conclude that PHTN compromises PA SMC O 2 sensing, alters intracellular Ca 2+ homeostasis, and changes the predominant ion channel that determines basal [Ca 2+ ] i from K Ca to K v .