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Departments of Physiology and Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298
Regulation of adenylyl cyclase type
V/VI and cAMP-specific, cGMP-inhibited phosphodiesterase (PDE) 3 and
cAMP-specific PDE4 by cAMP-dependent protein kinase (PKA) and
cGMP-dependent protein kinase (PKG) was examined in gastric smooth
muscle cells. Expression of PDE3A but not PDE3B was demonstrated by
RT-PCR and Western blot. Basal PDE3 and PDE4 activities were present in
a ratio of 2:1. Forskolin, isoproterenol, and the PKA activator
5,6-dichloro-1-
-D-ribofuranosyl benzimidazole
3',5'-cyclic monophosphate, SP-isomer, stimulated PDE3A phosphorylation
and both PDE3A and PDE4 activities. Phosphorylation of PDE3A and
activation of PDE3A and PDE4 were blocked by the PKA inhibitors
[protein kinase inhibitor (PKI) and H-89] but not by the PKG
inhibitor (KT-5823). Sodium nitroprusside inhibited PDE3 activity and
augmented forskolin- and isoproterenol-stimulated cAMP levels; PDE3
inhibition was reversed by blockade of cGMP synthesis. Forskolin
stimulated adenylyl cyclase phosphorylation and activity; PKI blocked
phosphorylation and enhanced activity. Stimulation of cAMP and
inhibition of inositol 1,4,5-trisphosphate-induced Ca2+
release and muscle contraction by isoproterenol were augmented additively by PDE3 and PDE4 inhibitors. The results indicate that PKA
regulates cAMP levels in smooth muscle via stimulatory phosphorylation of PDE3A and PDE4 and inhibitory phosphorylation of adenylyl cyclase type V/VI. Concurrent generation of cGMP inhibits PDE3 activity and
augments cAMP levels.
protein kinase A; phosphodiesterase; cyclic nucleotides; relaxation
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