AJP - Heart and Circulatory Physiology, Vol 266, Issue 4 1416-H1421, Copyright © 1994 by American Physiological Society

ARTICLES

Acute reductions in PO2 depolarize pulmonary artery endothelial cells and decrease [Ca2+]i

T. Stevens, D. N. Cornfield, I. F. McMurtry and D. M. Rodman
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.

Whereas pulmonary artery endothelial cells (PAECs) are sensitive to oxygen, neither the effect of an acute reduction in PO2 on PAEC membrane potential nor its effect on intracellular free Ca2+ ([Ca2+]i) is known. We hypothesized that in confluent primary cultures of PAECs, an acute decrease in PO2 would depolarize the cell membrane, inhibit Ca2+ influx, and reduce [Ca2+]i. To test this hypothesis, the membrane-sensitive fluorophore bis (1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4, 1 microM) and [Ca2+]i-sensitive probe fura 2 (3 microM) were used. A decrease in PO2 from 125 to 35 mmHg caused membrane depolarization and a 60 +/- 8% (data are means +/- SE) reduction in Ca2+ influx, estimated by manganese quenching of fura 2 fluorescence. While basal [Ca2+]i was 79 +/- 5 nM in normoxic cells, it decreased to 31 +/- 2 nM after 15 min of hypoxia. Decreasing the electrochemical gradient for Ca2+ entry with either low extracellular Ca2+, the K+ channel blockers tetraethylammonium or charybdotoxin, or blockade of Ca2+ entry with lanthanum decreased [Ca2+]i by 54-71% of that observed during an acute reduction in PO2. These results demonstrate that an acute reduction in PO2 1) depolarizes PAECs, 2) reduces Ca2+ influx, and 3) decreases [Ca2+]i, and that a similar reduction in [Ca2+]i was observed with interventions designed to reduce the electrochemical driving force for Ca2+ entry.

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