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Dexfenfluramine causes a transient increase in [Ca2+]i similar to that elicited by endothelin-1 (ET-1).In comparison to the response to endothelin-1, the response to dexfenfluramine is less sensitive to extracellular calcium chelation by EGTA and more sensitive to sarcoplasmic reticulum calcium depletion by caffeine. A-II is angiotensin II. [Ca2+]i was measured by dual spectroscopy using fluorescent calcium indicator, fura 2, from Molecular Probes. |
We wanted to know which of the many types of potassium channels
is closed by hypoxia in the pulmonary circulation, thus leading
to hypoxic pulmonary vasoconstriction. We tested the antibodies
against one of the most likely candidate channels, Kv1.5. We found
that the antibodies reduced the increase in intracellular calcium
([Ca2+]i), caused in pulmonary artery smooth muscle cells by hypoxia,
and reduced hypoxic pulmonary vasoconstriction in isolated lungs.
This indicates that the Kv1.5 channel is important in the mechanism
of hypoxic pulmonary vasoconstriction.
[Ca2+]i was measured in cultured rat resistance pulmonary arterial smooth
musle cells by the dual-excitation microfluorometry using the
fluorescent calcium indicator, fura 2 (from Molecular Probes). The antibody against a different potassium channel, Kv2.1,
is without effect. The right panel shows four subsequent responses
of isolated rat lungs to hypoxia, one just before and three after the addition of the
antibody or its vehicle alone into the perfusate, expressed as
% of the last response before the addition.
Antibodies against the Kv1.5 potassium channels (Upstate Biotechnology)
selectively inhibit the rise in [Ca2+]i caused in pulmonary artery smooth muscle cells by hypoxia (left)
and hypoxic vasoconstriction in isolated rat lungs (right).
*P<0.05; **P<0.01.
Our PhD student, Tomas Kucera, MD and I are currently working
on comparisons of the pressure-flow curves in isolated perfused rat lungs acquired by controlling pressure and measuring flow with those
obtained by controlling flow and measuring pressure. We started
to test the hypothesis that normal pulmonary vessels do not respond
to increased flow by vasoconstriction (unlike for example renal
or brain vessels), but they do in pulmonary hypertension, making
it more serious.
I am preparing some studies in perfused human placental cotyledon.
If it goes well, I will post it here.
Last modified: June 22, 1997
