Effects of protein kinase c down-regulation on norepinephrine- and
prostaglandin f-induced contraction in rat aorta.
Rapoport, Robert M., Anita K. Campbell, and Eulalia Bazan.
Department of Pharmacology and Cell Biophysics, College of
Medicine, University of Cincinnati, and Veterans Affairs Medical
Center, 231 Bethesda Avenue, Cincinnati, OH 45267-0575
APStracts 2:0090H, 1995.
The purpose of this study was to investigate, through phorbol ester
-induced protein kinase C (PKC) down-regulation, the role of PKC in
the regulation of [alpha]-adrenergic agonist- and prostaglandin
(PG)F2[alpha]-induced contraction in vascular smooth muscle. In rat
aorta, long-term phorbol ester exposure [10 [mu]M phorbol dibutyrate
(PDB) for 17h], a procedure that decreased PKC activity by greater
than 95%, and maximal phorbol myristate acetate (PMA)-induced
contraction by approximately 75%, decreased tissue sensitivity to
norepinephrine (NE) and PGF2[alpha] 2.8- and 4.6-fold, respectively,
while maximal contraction was not significantly decreased. In
contrast, long-term phorbol ester exposure did not alter tissue
sensitivity to KCl, while maximal KCl contraction was decreased by
40%. Long-term phorbol ester exposure, as well as short-term phorbol
ester exposure (1 [mu]M PMA for 1h), abolished the initial transient
NE contraction elicited in Ca2+-free solution. In contrast, long-term
phorbol ester exposure did not alter the plateau NE or PGF2[alpha]
contraction elicited in Ca2+-free solution. Short-term phorbol ester
exposure of PKC down-regulated tissues potentiated the plateau
PGF2[alpha] contraction elicited in Ca2+-free solution, although the
magnitude of potentiation was less than that observed in non-PKC
down-regulated tissues. These results suggest that PKC that is
subject to phorbol ester-induced down-regulation 1) serves as a
positive modulator of the extracellular Ca2+-dependent component of
the NE- and PGF2[alpha]-induced contraction; 2) serves as a negative
modulator of the component of the NE-induced contraction dependent on
intracellular Ca2+ release, i.e., the transient NE contraction
elicited in the absence of extracellular Ca2+, and 3) does not
modulate the component of the NE- and PGF2[alpha]-induced contraction
independent of both extracellular Ca2+ and intracellular Ca2+
release, i.e., the plateau contraction to PGF2[alpha] and NE elicited
in the absence of extracellular Ca2+.
Received 12 October 1994; accepted in final form 21 February
1995.
APS Manuscript Number H912-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.