Actions of ketamine, phencyclidine and MK‐801 on NMDA receptor currents in cultured mouse hippocampal neurones.

Abstract

SUMMARY1. Stable N-methyl-D-aspartic acid (NMDA) receptor-mediated currents in cultured mouse hippocampal neurones were evoked by 20 ms pressure pulse applications of L-aspartate, repeatedly applied at 30 or 40 s intervals, to the cell body region of the neurone. We have characterized the voltage-and use-dependent blockade of the currents by three dissociative anaesthetics: ketamine, phencyclidine (PCP) and MK-801 in mouse hippocampal neurones grown in dissociated tissue culture.2. We have used a simple model of the blockade, based on the 'guarded receptor hypothesis' to interpret our data. The model assumes that receptors are maximally activated at the peak of the response with an open probability (PO) approaching 1, that there is no desensitization and that the blocking drug only associates with, or dissociates from, receptor channels which have been activated by agonist (e.g. open channels).3. The model allows us to estimate forward and reverse rate constants for binding of the blockers to open channels from measurements of the steady-state level of blockade and the rate of change of the current amplitude per pulse during onset and offset of blockade. As predicted by the model, the estimated reverse rate was independent of blocker concentration while the forward rate increased with concentration. Changing the level of positively charged ketamine (pKa 7 5) tenfold by changing pH from 6-5 to 8-5 caused a corresponding change in the forward rate while having no effect on the reverse rate. Most of the voltage dependence of the blockade could be accounted for by reduction of the reverse rate by depolarization.4. Estimated forward rate constants for ketamine, PCP and MK-801 were similar to one another when measured under similar conditions and were 3 x 104-3 x 105 M-1 s-1. Most of the differences in potency of the three blockers could be accounted for by differences in the reverse rate constants which were approximately 0-2, 0 03 and 0 003 s-1 for ketamine, PCP and MK-801, respectively.The estimated rate constants actually are the product of the rate constants and 1/PO. I 843616-2 J. F. MAcDONALD AND OTHERS Suggestions that maximum P. is much less than 1 for NMDA channels imply that both forward and reverse rate constants of blockade may in fact be larger than we have calculated. However, their magnitudes, relative to one another, are unaffected by this consideration. 5. The reverse rate constant of blockade increased at positive potentials. This increase was prevented when the neurone was loaded with N-methyl-D-glucamine, an impermeant cation which prevented outward currents. This observation suggests that the voltage-dependent blockade by dissociative anaesthetics is in fact current dependent and reflects displacement of anaesthetic molecules, bound to the vicinity of the outer mouth of the channel, by intracellular cations that move out of the cell via the channel at positive potentials. This suggestion is supported by the observation that the voltage dependence of the blockade by the neutral PCP analogue, 1-(1-...

Ketamine, But Not Phencyclidine, Selectively Modulates Cerebellar GABAAReceptors Containing α6 and δ Subunits

“…Binding and electrophysiological studies have demonstrated that PCP and MK-801 are superior noncompetitive inhibitors of, and have markedly higher affinity for, NMDA receptors than ketamine (Chen et al, 1959;Johnstone et al, 1959;Chen, 1965;McCarthy et al, 1965;Wong et al, 1986;MacDonald et al, 1991;Rogawski and Wenk, 2003). In addition, MK-801 block can occur across different membrane potentials, whereas PCP and ketamine inhibit NMDA receptors predominately at depolarized potentials (Halliwell et al, 1989;Dravid et al, 2007).…”

“…MK-801, a dissociative anesthetic chemically unrelated to PCP, possesses an even greater affinity to, and inhibits NMDA receptors with higher potency than PCP (Wong et al, 1986;Huettner and Bean, 1988;MacDonald and Nowak, 1990;MacDonald et al, 1991). Furthermore, the blocking action of MK-801 on the NMDA receptor is less dependent on the membrane potential than ketamine or PCP (Halliwell et al, 1989;Dravid et al, 2007).…”

“…It has been established that dissociative anesthetics are noncompetitive inhibitors of NMDA excitatory ligand-gated ion channels (Lodge and Anis, 1982;Anis et al, 1983;MacDonald et al, 1987MacDonald et al, , 1991ffrench-Mullen and Rogawski, 1989;Rogawski and Wenk, 2003). These drugs also modulate the activity of nicotinic acetylcholine, muscarinic, and opioid receptors, and voltage-gated ion channels, but at significantly higher concentrations than needed to block NMDA receptors (Finck and Ngai, 1982;Ramoa et al, 1990;Hustveit et al, 1995;Hirota and Lambert, 1996;Scheller et al, 1996;Brau et al, 1997;Furuya et al, 1999;Flood and Krasowski, 2000;Yamakura et al, 2000;Schnoebel et al, 2005).…”

Underlying mechanism for NMDA receptor antagonism by the anti-inflammatory drug, sulfasalazine, in mouse cortical neurons

“…We previously proposed that SULFA acts as a potential open channel blocker (Ryu et al, 2003), but further experiments, reports and careful consideration have ruled out this possibility. Several channel blockers, including MK-801 (Halliwell et al, 1989), ketamine (MacDonald et al, 1991), and memantine (Chen and Lipton, 1997) have shown activity-and voltage-dependencies inconsistent with those observed for SULFA (Figs. 2B and 8).…”

Synergism between Topiramate and Budipine in Refractory Status Epilepticus in the Rat

“…In contrast, low-affinity NMDA-receptor antagonists such as budipine [K i = 12 µM (41)] are clinically tolerated and are not typically associated with psychotomimetic side effects (42) on account of their fast dissociation kinetics [offset rate of budipine, 0.63 s −1 (43)] that are ≥2 orders of magnitude faster than that of MK-801 (44). During strong depolarization, low-affinity NMDA-receptor ion channel antagonists are thought to mimic Mg 2+ by rapidly leaving the ion channel after its physiologic activation, but differ from Mg 2+ in that it does not exit the ion channel after moderate prolonged synaptic depolarization, as seen with chronic excitotoxicity (40).…”