clozapine and chelerythrine

We have previously shown that the atypical antipsychotic drug clozapine facilitates N-methyl-D-aspartate (NMDA)- and electrically evoked responses in pyramidal cells of the medial prefrontal cortex (mPFC). In the present study, we investigated the role of protein kinase C (PKC) in the action of clozapine. Bath administration of the PKC activator phorbol-12-myristate 13-acetate (PMA), but not the inactive isomer 4alpha-PMA, significantly enhanced the NMDA-evoked inward current and electrically evoked excitatory postsynaptic currents. Chelerythrine, a selective blocker of PKC, completely prevented the potentiating action produced by either clozapine or PMA on these currents in the mPFC cells. Intracellular injection of the PKC inhibitor PKC-I, but not the control substance PKC-S, through the recording electrode totally blocked clozapine's potentiating effect, indicating that a post-synaptic expressed PKC is critically involved in the augmenting action of clozapine on NMDA-evoked currents. Of the PKC inhibitor PKC-I, but not the control substance PKC-S, through the recording electrode totally blocked clozapine's potentiating effect, indicating that a post-synaptic expressed PKC is critically involved in the augmenting action of clozapine on NMDA-evoked currents. To further test the role of PKC in mediating the augmenting action of clozapine, we performed experiments in PKCgamma mutant and wild-type mice. In contrast to results in pyramidal cells from rats or wild-type mice, neither clozapine nor PMA was able to potentiate NMDA-induced currents in the mPFC from the PKCgamma mutant mice. Taken together, these results suggest that the PKC signal transduction pathway is critically involved in the facilitating action of clozapine on the NMDA-induced responses in pyramidal cells of the mPFC.

Topics: Alkaloids; Animals; Benzophenanthridines; Clozapine; Drug Interactions; Electric Stimulation; Electrophysiology; Enzyme Activators; Enzyme Inhibitors; Evoked Potentials; Excitatory Amino Acid Agonists; Excitatory Postsynaptic Potentials; Fluorobenzenes; GABA Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; Mice; Mice, Knockout; Mice, Mutant Strains; N-Methylaspartate; Peptide Fragments; Phenanthridines; Phorbols; Piperidines; Protein Kinase C; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Serotonin Antagonists; Tetradecanoylphorbol Acetate; Time Factors

Intracellular recordings were obtained from rat presumed jaw-closing motoneurons in slice preparations to investigate the involvement of the serotonin(7) (5-HT(7)) receptors in serotonergic inhibition of the postspike medium-duration afterhyperpolarization (mAHP) and enhancement of the afterdepolarization (ADP). 5-HT-induced suppression of the mAHP and enhancement of the ADP were mimicked by application of the 5-HT(1A/7) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and antagonized by the 5-HT(2/6/7) receptor antagonist clozapine, whereas the 5-HT(2) receptor agonist alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT) did not affect the mAHP and ADP. 8-OH-DPAT-induced attenuation of the mAHP and enhancement of the ADP were also antagonized by clozapine and another 5-HT(2/6/7) receptor antagonist ritanserin, whereas the 5-HT(1A) receptor antagonist pindolol failed to block the 8-OH-DPAT-induced effects on the mAHP and ADP. 8-OH-DPAT-induced suppression of the mAHP and enhancement of the ADP were also antagonized by a protein kinase A (PKA) inhibitor H89, whereas 8-OH-DPAT could inhibit the mAHP and enhance the ADP in the presence of a protein kinase C (PKC) inhibitor chelerythrine. The 8-OH-DPAT-induced suppression of the mAHP was enhanced under raised [Ca(2+)](o) and this enhancement was reduced by chelerythrine. It is suggested that the 5-HT(7) receptors are involved in 5-HT-induced attenuation of the mAHP and enhancement of the ADP through activation of PKA, and the attenuation of mAHP through the 5-HT(7) receptors is enhanced under raised [Ca(2+)](o) by PKC activation.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Action Potentials; Alkaloids; Animals; Benzophenanthridines; Brain Stem; Calcium; Clozapine; Cyclic AMP-Dependent Protein Kinases; Electrophysiology; Enzyme Inhibitors; Isoquinolines; Jaw; Membrane Potentials; Motor Neurons; Phenanthridines; Pindolol; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Ritanserin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sulfonamides

Dopamine inhibits Na+ and water reabsorption in the rat cortical collecting duct (CCD) in the presence of arginine vasopressin (AVP). This inhibition appears to involve the D4 dopamine receptor isoform, which inhibits cAMP production; however, the D1A receptor, which stimulates cAMP production, is also expressed in the CCD. To discriminate between these opposing effects, we measured cAMP production in intact CCD segments. The basal rate of cAMP production ranged from 6.5 to 10 fmol/mm of tubule length over a 7-min incubation period, and it was unaffected by either dopamine or the D1A-specific agonist fenoldopam. AVP increased cAMP production to the range of 85-153 fmol . mm-1 . 7 min-1. Whereas neither 0.1 nor 1.0 microM fenoldopam affected AVP-dependent cAMP production, dopamine reduced it in a dose-dependent manner, achieving a maximum inhibition of 50% at 10 microM. This effect was reversed by the D4 receptor antagonist clozapine but not by pimozide or spiperone (antagonists of D2 and D3 receptors) or by calphostin C or chelerythrine (inhibitors of protein kinase C). We conclude that dopamine inhibits transepithelial Na+ transport and osmotic water permeability in the presence of AVP by inhibition of cAMP production, which is mediated by the D4 receptor isoform linked via the inhibitory G protein Gi.

Topics: Alkaloids; Animals; Arginine Vasopressin; Benzophenanthridines; Clozapine; Cyclic AMP; Dopamine; Dopamine Antagonists; Dopamine D2 Receptor Antagonists; Enzyme Inhibitors; Epinephrine; Fenoldopam; GTP-Binding Proteins; In Vitro Techniques; Kidney Cortex; Kidney Tubules, Collecting; Kinetics; Male; Naphthalenes; Phenanthridines; Pimozide; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, Dopamine D3; Receptors, Dopamine D4; Spiperone; Time Factors; Yohimbine