Journal of Neuroscience, Vol 8, 2447-2451, Copyright © 1988 by Society for Neuroscience
The effect of down regulation of protein kinase C on the inhibitory modulation of dorsal root ganglion neuron Ca2+ currents by neuropeptide Y
DA Ewald, HJ Matthies, TM Perney, MW Walker and RJ Miller
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Dorsal root ganglion (DRG) neurons cultured from neonatal rats contained
high concentrations of protein kinase C (PKC). Normally, the majority of
the enzyme activity was found in the cytosol and considerably less was
associated with the membrane fraction. Upon incubation with the phorbol
ester phorbol dibutyrate (PDBu, 10(-6) M) for 20 min, PKC activity
increased in the membrane-associated fraction and decreased in the
cytoplasmic fraction. Longer incubations with phorbol ester also induced a
decline in membrane-associated PKC activity. If incubations were continued
for periods of over 10 hr, both membrane and cytosolic PKC activity
declined essentially to zero. Down- regulation of PKC had no effect on the
number or affinity of 125I- neuropeptide Y (NPY) binding sites on DRG cells
or on the absolute magnitude of the DRG Ca2+ current. However, the ability
of NPY to inhibit the DRG Ca2+ current was greatly reduced. When sustained
Ca2+ currents were evoked from depolarized holding potentials (-40 mV), all
concentrations of NPY (10(-10)-10(-7) M) were less effective. In contrast,
higher concentrations of NPY still blocked the transient portion of the DRG
Ca2+ current evoked from hyperpolarized holding potentials. These results
support the suggestion that PKC is involved in the inhibitory modulation of
DRG Ca2+ currents by neurotransmitters. The precise role of PKC may vary
depending on the type of Ca2+ channel involved.