Protein kinase C involvement in maintenance and modulation of noradrenaline release in the mouse brain cortex.
1. The role of protein kinase C in the modulation of noradrenaline release was investigated in mouse cortical slices which were pre-incubated with [3H]-noradrenaline. The aim was to investigate the hypothesis that protein kinase C is activated during high levels of transmitter release to maintain transmitter output. 2. The protein kinase C activators, phorbol myristate acetate (0.01-0.3 microM) and to a greater extent 4 beta-phorbol 12,13-dibutyrate (0.01-0.3 microM) significantly enhanced stimulation-induced noradrenaline release whereas 4 alpha-phorbol 12,13-dibutyrate (0.1 microM) which does not activate protein kinase C was without effect. The effect of the protein kinase C activator, phorbol myristate acetate, on noradrenaline release was attenuated by the protein kinase C inhibitor, polymyxin B (21 microM) which by itself inhibited stimulation-induced noradrenaline release. 3. Protein kinase C was down-regulated by 10 h exposure of the cortical slices to 4 beta-phorbol 12,13-dibutyrate (1 microM). In this case the facilitatory effect of 4 beta-phorbol 12,13-dibutyrate (0.1 microM) on noradrenaline release was abolished as was the inhibitory effect produced by polymyxin B. This indicates that polymyxin B was acting selectively at protein kinase C. 4. The inhibitory effect of polymyxin B on noradrenaline release, when expressed as a percentage of the appropriate frequency control, was constant at 1, 5 and 10 Hz. Furthermore, the ratio of release at 5 Hz to that at 10 Hz was not altered by protein kinase C down-regulation, indicating that there is no additional effect of protein kinase C at higher stimulation frequencies. 5. When transmitter release was elevated by blocking alpha 2-adrenoceptor auto-inhibition with idazoxan (0.1 microM) or K+ channels with tetraethylammonium (300 microM), the elevation in transmitter release was significantly attenuated by protein kinase C down-regulation, suggesting an involvement of protein kinase C. 6. We conclude that protein kinase C is involved in the modulation of noradrenaline release over a wide range of stimulation frequencies, in addition to a role when noradrenaline release is elevated by presynaptic mechanisms.
Schroeder
G E
GE
Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia.
Kotsonis
P
P
Musgrave
I F
IF
Majewski
H
H
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D004146:Dioxanes / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004558:Electric Stimulation; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019329:Idazoxan; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D009638:Norepinephrine / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors; D014316:Tritium
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004791:Enzyme Inhibitors; D007093:Imidazoles; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D014316:Tritium; D015240:Phorbol 12,13-Dibutyrate; D019789:Tetraethylammonium; D011493:Protein Kinase C; D011112:Polymyxin B; D009638:Norepinephrine; D019329:Idazoxan