Regulation of native GABAA receptors by PKC and protein phosphatase activity.
OBJECTIVE
Protein kinase C (PKC) modulation of ionotropic receptors is a common mechanism for regulation of channel function. The effects of PKC and phosphatase activation on native gamma-aminobutyric acid (GABA(A)) receptors in adult brain are unknown. Previous studies of recombinant GABA(A) receptors have provided evidence that PKC activation inhibits receptor function, whereas other studies suggest that PKC either increases or does not alter GABA(A) receptor function. The present study explored (a) the effects of PKC and phosphatase activity on GABA-mediated (36)Cl(-) uptake in cerebral cortical synaptoneurosomes and (b) the effect of PKC activity on muscimol-induced loss of righting reflex (LORR) in adult rats.


METHODS
GABA(A) receptor function in vitro was measured by muscimol-induced (36)Cl(-) uptake into cerebral cortical synaptoneurosomes. The in vivo effect of PKC on GABA(A)-mediated function was measured by intracerebroventricular (i.c.v.) injection of 4-beta-phorbol-12,13-dibutyrate (PDBu) or calphostin C followed by determination of muscimol-induced LORR.


RESULTS
Adenosine triphosphate (ATP) and PDBu produced a concentration-dependent and specific reduction in muscimol-stimulated (36)Cl(-) uptake that was blocked by the PKC inhibitor calphostin C. Both adenosine diphosphate and 4alphaPDBu were ineffective. Phosphatase inhibition produced similar inhibition of muscimol responses. Furthermore, i.c.v. administration of PDBu and calphostin C produced opposing effects on both the onset and the duration of muscimol-induced LORR in rats.


CONCLUSIONS
The present study provides evidence that PKC activation reduces GABA(A) receptor function in native receptors both in vitro and in vivo. Phosphatase inhibitors decrease muscimol-mediated Cl(-) uptake in GABA(A) receptors demonstrating coordinated regulation of native receptors by PKC and phosphatases.
Kumar
Sandeep
S
Department of Psychiatry, Bowles Center for Alcohol Studies, UNC School of Medicine, Chapel Hill, NC 27599, USA.
Khisti
Rahul T
RT
Morrow
A Leslie
AL
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D002712:Chlorides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D018755:GABA Agonists / Q000493:pharmacokinetics; D007554:Isotopes / Q000378:metabolism; D008297:Male; D052998:Microcystins; D009118:Muscimol / Q000493:pharmacokinetics; D009281:Naphthalenes / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000493:pharmacokinetics; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D002712:Chlorides; D004791:Enzyme Inhibitors; D018755:GABA Agonists; D007554:Isotopes; D052998:Microcystins; D009281:Naphthalenes; D010456:Peptides, Cyclic; D011963:Receptors, GABA-A; D009118:Muscimol; D015240:Phorbol 12,13-Dibutyrate; D005680:gamma-Aminobutyric Acid; D000244:Adenosine Diphosphate; C078588:microcystin; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; C058819:calphostin C