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)