Differential effects of protein kinase C activation on 5-HT1A receptor coupling to Ca2+ and K+ currents in rat serotonergic neurones.
1. Activation of the enzyme protein kinase C (PKC) partially uncouples receptors from the inhibition of Ca2+ current. We have studied the effect of PKC activation on 5-HT1A receptor coupling of Ca2+ currents and 5-HT-induced K+ current (IK,5-HT) in acutely isolated adult rat dorsal raphe neurones. 2. The phorbol ester 4 beta-phorbol 12-myristate, 13-acetate (PMA; 1 microM) did not significantly alter the peak Ca2+ current. A maximal dose of 5-HT inhibited Ca2+ current on average by 52%; after application of PMA, the inhibition was only 30% and the effect was irreversible for the duration of the experiment. 3. The inactive phorbol ester 4 alpha-phorbol (1 microM) did not reduce the effectiveness of 5-HT. When the kinase inhibitor staurosporine (ST; 200 nM) was added, PMA reduced the effect of 5-HT by only 13.9%. ST partially prevented or reversed the effect of PMA, depending on the order of addition. 4. The voltage-dependent rate or re-inhibition by 5-HT was reduced by PMA, suggesting that fewer activated G-protein subunits are available to interact with Ca2+ channel after the action of PMA. 5. In contrast, PMA (1 microM) did not have a significant effect on IK,5-HT. 6. PKC activation has an inhibitory effect on one branch of the 5-HT1A receptor transduction fork, namely inhibition of Ca2+ influx, but not on the activation of IK,5-HT.
Department of Pharmacology, State University of New York, Health Science Center at Brooklyn 11203-2098, USA.
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Chen
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Penington
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D015221:Potassium Channels; D011985:Receptors, Serotonin; D012701:Serotonin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate