AJP - Lung Cellular and Molecular Physiology, Vol 266, Issue 4 469-L475, Copyright © 1994 by American Physiological Society
Acute hypoxia causes membrane depolarization and calcium influx in fetal pulmonary artery smooth muscle cells
D. N. Cornfield, T. Stevens, I. F. McMurtry, S. H. Abman and D. M. Rodman
Department of Pediatrics, Children's Hospital, Denver, Colorado.
Changes in oxygen tension in the perinatal period contribute to high
pulmonary vascular tone in the fetus and the decline in resistance that
occurs at birth. Distal pulmonary artery smooth muscle cells (PASMC)
isolated from late-gestation ovine fetuses respond to acute hypoxia with an
increase in cytosolic calcium concentration ([Ca2+]i) dependent on Ca2+
entry. The purpose of this study is to determine 1) whether acute hypoxia
results in PASMC membrane depolarization, 2) whether Ca2+ entry was through
voltage-operated calcium channels (VOCC), 3) the contribution of
Ca(2+)-induced Ca2+ release (CICR) to the hypoxic response, and 4) whether
a subset of K+ channels might serve as oxygen sensors in fetal PASMC. We
used microfluorimetry on subconfluent monolayers of PASMC in primary
culture loaded with either a membrane potential-sensitive dye,
bis(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4; DPASMC), to
estimate membrane potential, or the Ca(2+)-sensitive fluorophore, fura 2,
to measure [Ca2+]i. Hypoxia increased fluorescence from PASMC loaded with
DiBAC4, consistent with membrane depolarization. Verapamil (an inhibitor of
VOCC) attenuated, and BAY K 8644 (a VOCC facilitator) potentiated, the
hypoxia-induced increase in [Ca2+]i, respectively. The hypoxic response was
transient after treatment with ryanodine (10(-7) M), a blocker of calcium
release from intracellular stores. Charybdotoxin (10(-7) M), an inhibitor
of Ca(2+)-activated K+ channels, almost doubled [Ca2+]i, whereas
glibenclamide (10(-5) M), an ATP-sensitive K(+)-channel antagonist, had no
effect.(ABSTRACT TRUNCATED AT 250 WORDS)
