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Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, Georgia 30912
The role of
Ca2+-activated
K+-channel, ATP-sensitive
K+-channel, and delayed rectifier
K+-channel modulation in the
canine pulmonary vascular response to protein kinase C (PKC) activation
was determined in the isolated blood-perfused dog lung. Pulmonary
vascular resistances and compliances were measured with vascular
occlusion techniques. The PKC activators phorbol 12-myristate
13-acetate (PMA; 10
7 M) and
thymeleatoxin (THX; 10
7 M)
significantly increased pulmonary arterial and pulmonary venous resistances and pulmonary capillary pressure and decreased total vascular compliance by decreasing both microvascular and large-vessel compliances. The Ca2+-activated
K+-channel blocker
tetraethylammonium ions (1 mM), the ATP-sensitive K+-channel inhibitor glibenclamide
(10
5 M), and the delayed
rectifier K+-channel blocker
4-aminopyridine (10
4 M)
potentiated the pressor response to both PMA and THX on the arterial
and venous segments and also further decreased pulmonary vascular
compliance. In contrast, the ATP-sensitive
K+-channel opener cromakalim
(10
5 M) attenuated the
vasoconstrictor effect of PMA and THX on both the arterial and venous
vessels. In addition, membrane depolarization by 30 mM KCl elicited an
increase in the pressor response to PMA. These results indicate that
pharmacological activation of PKC elicits pulmonary vasoconstriction.
Closure of the Ca2+-activated
K+ channels, ATP-sensitive
K+ channels, and delayed rectifier
K+ channels as well as direct
membrane depolarization by KCl potentiated the response to PMA and THX,
indicating that K+ channels
modulate the canine pulmonary vasoconstrictor response to PKC activation.
pulmonary vascular resistance; pulmonary vascular compliance; thymeleatoxin
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