Chronic intrauterine pulmonary hypertension compromises fetal pulmonary artery smooth muscle cell O2 sensing

Division of Pediatric Pulmonology and Critical Care Medicine, Departments of 1 Pediatrics, 2 Surgery, and 3 Physiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455 Submitted 1 April 2003 ; accepted in final form 24 June 2003 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 P O 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 . fetus; cytosolic calcium; potassium channel Address for reprint requests and other correspondence: B. C. Linden, MMC 742, Univ. of Minnesota School of Medicine, 420 Delaware St. SE, Minneapolis, MN 55455 (E-mail: lind0186{at}umn.edu ).