AJP - Cell Physiology, Vol 258, Issue 4 C610-C617, Copyright © 1990 by American Physiological Society
Regulation of angiotensin II binding sites in neuronal cultures by protein kinase C
C. J. Kalberg and C. Sumners
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610.
The radioligand binding of 125I-angiotensin II (ANG II) and calcium
phospholipid-dependent protein kinase C (PKC) activity were measured to
study the specificity and mechanisms of PKC involvement in the regulation
of ANG II-specific binding site expression in neuronal cultures prepared
from the brains of 1-day-old rats. Previously, PKC-activating phorbol
esters were shown to increase the specific binding of 125I-ANG II in
neuronal cultures. However, phorbol esters have many biological effects,
which may nonspecifically act to increase 125I-ANG II-specific binding. In
the present study, mezerein and teleocidin A, two activators of PKC that
are chemically unrelated to phorbol esters, increased the specific binding
of 125I-ANG II in a dose- and time-dependent manner with 50% effective dose
(ED50) values of 32 and 79 nM, respectively. The PKC antagonist H-7 dose
dependently inhibited phorbol 12-myristate 13-acetate (TPA)-stimulated
increases in 125I-ANG II binding, whereas downregulation of PKC activity by
chronic phorbol ester incubations of 24 and 48 h prevented TPA-stimulated
increases in 125I-ANG II-specific binding. TPA (0.8 microM), mezerein (0.76
microM), and teleocidin A (0.5 microM) all caused a rapid translocation of
PKC activity from the cytosol to the particulate fraction by 15 min.
Temporally, the maximal stimulation of PKC translocation by mezerein,
teleocidin A, and TPA preceded their ability to stimulate maximal 125I-ANG
II-specific binding. Taken together, these results suggest that PKC is
directly involved in the stimulation of ANG II-specific binding site
expression and that translocation of PKC is a prerequisite for the
increased expression of ANG II binding sites.
