The effect of down regulation of protein kinase C on the inhibitory modulation of dorsal root ganglion neuron Ca2+ currents by neuropeptide Y.
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.
Ewald
D A
DA
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Matthies
H J
HJ
Perney
T M
TM
Walker
M W
MW
Miller
R J
RJ
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D009474:Neurons / Q000201:enzymology / Q000502:physiology*; D009478:Neuropeptide Y / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism* / Q000502:physiology; D051381:Rats
D009478:Neuropeptide Y; D011493:Protein Kinase C; D002118:Calcium